Dr. Rebecca Dekker – 00:00:00:

Hi everyone, on today’s podcast we’re going to talk about the updated evidence on diagnosing Gestational Diabetes. Welcome to the Evidence Based Birth® Podcast. My name is Rebecca Dekker, and I’m a nurse with my PhD and the founder of Evidence Based Birth®. Join me each week as we work together to get evidence-based information into the hands of families and professionals around the world. As a reminder, this information is not medical advice. See ebbirth.com/disclaimer for more details. Hi, everyone. Welcome to today’s episode of the Evidence Based Birth® Podcast. For this special episode all about gestational diabetes, I have a co-host today. My co-host name is Dr. Morgan Richardson Cayama, and I am so excited to talk with her today about the updated evidence on diagnosing Gestational Diabetes. You will be able to access all the information from this podcast, including scientific references, our updated full-length Signature Article, and a free two-page handout by visiting ebbirth.com/diagnosinggdm. As a quick content note before we get started, in today’s episode we will be talking about serious health complications for birthing people and babies, and we will also be mentioning sizeism and fat phobia. So Dr. Morgan has her PhD and Masters in Public Health and is a member of the EBB research team. Morgan, I’m so happy to have you back with us.

Dr. Morgan Richardson Cayama – 00:01:34:

Yeah. Thanks so much for having me. I am really looking forward to diving into a lot of the research that we found on this topic. And I know there’s a lot of interest and curiosity and this impacts a lot of people. So I’m excited to join.

Dr. Rebecca Dekker – 00:01:45:

Yeah. We get lots of questions sent to us about Gestational Diabetes and you’ve been with us, since early 2023. You’ve been co-host and guest on a few podcast episodes now, including episode 334, which was a huge hit all about the ARRIVE trial and elective induction at 39 weeks and episode 343 on the top 10 evidence-based strategies for lowering the risk of having a Cesarean. And for the past few months, you’ve been working with me to update the Evidence Based Birth® Signature Article on diagnosing GDM. So the last update on this topic was back in 2019. And the research in this area has sort of exploded in the last five to six years. So for this update, we’ve added a lot of new content and research on this topic that we’re excited to share. So Gestational diabetes is a big topic and diagnosing Gestational diabetes specifically is surprisingly complex and quite controversial. So you’re going to be learning more today as we make our way through this episode. We’ll be focusing on defining Gestational diabetes, explaining the potential health risks, and we’ll be discussing the evidence on screening and diagnosis, including the evidence on alternatives to the traditional Glucola drink that is used to diagnose Gestational diabetes. As a note, we do have a different Signature Article on inducing for Gestational diabetes. If you’re wondering about the evidence on my provider is recommending I schedule induction, we have a separate article on that. That’s a whole other topic in itself. And you can find that at ebbirth.com/inducinggdm. And we have plans to update that article since it’s kind of a companion to this one sometime in the next year. All right, so Morgan, can you start off by giving us a little bit of a background on Gestational diabetes?

Dr. Morgan Richardson Cayama – 00:03:42:

Yeah, sure. So Gestational diabetes mellitus or mellitus, it’s often referred to as GDM. And this is high blood sugar that develops during pregnancy. And so without getting too much into the physiology of the process, which we absolutely go into a lot more detail about in the Signature Article, it is important to know that everyone experiences metabolic changes during pregnancy. And they experience some level of insulin resistance. This is pretty common and pretty normal across all pregnancies. And historically, this insulin resistance has helped prioritize the movement of sugar and nutrients to the fetus instead of the pregnant person, which helps, of course, promote healthy fetal growth and development. And it actually served us pretty well historically when we typically had less access to food or when you think about periods of famine. But in pregnancies without GDM, the body’s insulin response is still able to kind of overcome that resistance by producing more insulin. But in pregnancies with GDM, there can just be too much insulin resistance or too little of an insulin response or even a combination of both. And this is what causes glucose or sugar to build up in that blood until it reaches abnormally high levels. And this is called hyperglycemia. And so as we’ll talk more about later, screening for GDM and diabetes in general involves measuring blood sugar levels. Gestational diabetes also is not the same thing as type 1 or type 2 diabetes. And diagnostic thresholds for Gestational diabetes are actually lower for GDM than type 2, although management and treatment of GDM is pretty similar to type 2 diabetes. And pregnant people who develop GDM are also actually at higher risk for developing type 2 diabetes later in life. So how common is Gestational diabetes, Rebecca? And what are some of the biggest risk factors that we need to be aware of?

Dr. Rebecca Dekker – 00:05:30:

Okay, so one of the reasons I think this is such a hot topic is because Gestational diabetes is one of the most common health problems of pregnancy. And as we’ve hinted at already, there’s a lot of debate over the best way to diagnose it and how to decide who has Gestational diabetes. And actually rates of GDM change depending on the test that’s used and the cutoff criteria used to kind of define who has Gestational diabetes. So most care providers around the world use something called the IADPSG criteria, which stands for International Association of Diabetes and Pregnancy Study Groups. So using these international criteria, researchers have looked at data from more than 40 countries and they estimated a global rate of Gestational diabetes of about 14%. And that was in the year 2022. So that’s more than one in 10 pregnant people has Gestational diabetes around the world. Now, in the United States and Canada, however, care providers follow different criteria for diagnosing Gestational diabetes. They use something either called the Carpenter-Coustan criteria or the National Diabetes Data Group criteria. And in 2020, the last year we kind of have national data for this, around 8% of pregnant people in the U.S. needed treatment for Gestational diabetes. However, it’s been pretty much confirmed in the research that rates of GDM in the United States would double if we switch to those international criteria. Now, rates in general, regardless of which criteria you use, have been increasing around the world. And this might have to do with an increase in the number of people with risk factors for GDM. Now, before I go on, I do want to acknowledge the role that sizeism and fat phobia play in the way that people with bigger bodies are treated in health care in general and in maternity care. So health care providers sometimes show bias and can shame and stigmatize people with larger bodies. And even though most people with larger bodies will not develop Gestational diabetes in pregnancy, they may be incorrectly labeled or treated as if they have it, even if later on they go on to have tests that show they do not have it. That all being said, one of the most commonly referred to risk factors for GDM is having a bigger body, which most studies define as a pre-pregnancy body mass index, or BMI, of 25 or above, or 23 or above for Asian Americans in the U.S.. So BMI, as many of you know, is a flawed measurement, and this has been acknowledged its flaws by the American Medical Association, but it’s still commonly used in research. And although rates of Gestational diabetes are highest among those with higher BMIs, someone who is not plus size can still get GDM. In fact, about 25% of those diagnosed with GDM have a pre-pregnancy BMI below 25. You might also be at higher risk for GDM, if you are older or advanced maternal age, typically defined as being 35 to 40 or older. If you have a history of Gestational diabetes in a previous pregnancy, or if you have a history of insulin resistance, heart disease, or high blood pressure. If you’ve had a history of birth complications, like having a large for gestational age baby, or having a preterm birth previously. If you have a close relative with diabetes, or if you belong to a racial or ethnic group at increased risk. So in the U.S., this would include people who are African American, Hispanic, or Latina, Alaskan Natives, Native Americans, South Asians, Native Hawaiians or Pacific Islanders, or those of Middle Eastern descent. So there are a few theories as to why some of these ethnic groups are at higher risk for Gestational diabetes. There was a study led by Gitlin et al, and they noticed that differences in GDM prevalence across geographic regions might be due to differences in culture that leads to diet and activity levels, genetics, economic stability, and healthcare access. They also note that babies whose gestational parent experienced undernutrition during pregnancy might also be more likely to experience challenges with insulin deficiency and resistance later in life, increasing your likelihood for GDM and for diabetes as an adult. So it’s a little bit complicated, but those are the risk factors. And like I said, it’s one of the most common problems in pregnancy. So Morgan, we know a little bit more about GDM. Can you tell us why is screening recommended? Like what is the purpose of doing the screening?

Dr. Morgan Richardson Cayama – 00:10:40:

Yeah, absolutely. So GDM or Gestational diabetes has been linked to higher rates of many poor outcomes. And just to name a few, that includes preeclampsia or a high blood pressure during pregnancy, first time Cesarean birth, preterm birth, having a large baby, newborn jaundice, newborn intensive care. And there are even some other ones that have been found in the research as well. So some studies have also found a higher risk again of type 2 diabetes in people who are diagnosed with Gestational diabetes, as well as heart disease and stroke later in their life. And studies have also found that higher risk of type 2 diabetes in offspring for people who were diagnosed with Gestational diabetes. So they might be at higher risk of developing diabetes as well later in their life. So one of the most famously cited studies that we talk about around Gestational diabetes is the Hyperglycemia and Adverse Pregnancy Outcomes, or HAPO study. And this study looked at the link between prenatal blood sugar and the risk of those four birth outcomes. So the study was published back in 2008, and it was a pretty big study that followed more than 23,000 pregnant people in nine different countries. These were people who were not previously diagnosed with diabetes. So everyone in this study was screened with a 75 gram oral glucose tolerance test or OGTT, you might’ve heard it called between 24 and 32 weeks of pregnancy. Now we’re going to talk more about those tests and OGTTs soon, but in this type of test, blood sugar levels are checked after fasting. And then again, after one and two hours after drinking 75 grams of glucose. So the researchers then compared differences in health outcomes between seven different categories of blood sugar levels across those three different time points for testing. So again, after fasting and after one or two hours. They found that the risk of many of these outcomes was highest among those with the highest blood sugar levels. So perhaps that’s not really surprising. But one of the biggest findings from this study was that relationship between someone’s blood sugar levels in pregnancy and the risk of poor outcomes was continuous, meaning there wasn’t really a specific cutoff or a line that they could draw for risk or what was considered low risk and high risk. So instead, every small increase in blood sugar levels, even within blood sugar ranges that were considered normal, resulted in an increased risk for worse health outcomes. And findings from this HAPO study are what formed the basis of the Gestational diabetes diagnostic cutoffs proposed by that IADPSG group that Rebecca just mentioned, which are used in many countries, again, around the world today.

Dr. Rebecca Dekker – 00:13:17:

So that’s such an important point, Morgan, that you said about the HAPO study, because that finding that there wasn’t a clear line where researchers can say this is normal blood sugar and this is abnormal. This is one reason why there’s so much controversy over how to best test for and diagnose GDM. And so that kind of brings me into the best methods for screening and testing for this condition. So most professional organizations or clinical guidance recommends that people be screened between 24 and 28 weeks of pregnancy. So this is something you’re typically doing in your second trimester. And the two most common screening tests are the one-step method and the two-step method. And both of them are going to use the oral glucose tolerance test or OGTT that you mentioned earlier. So the one-step method became the most common method around the world after the HAPO study. However, this method is not used in the U.S. or Canada typically. So with the one-step method, you have to fast for at least eight hours. You go in and have your blood drawn fasting to measure your fasting blood sugar level. You’re then given a 75 gram glucose drink and you have to consume that pretty quickly. And then your blood is drawn one and two hours after you’ve consumed the drink. So this is three blood draws. In contrast to that, the two-step method is what we commonly use in the United States and Canada. So this approach involves an initial screening OGTT. And if you test positive, then you’ll have a follow-up diagnostic OGTT. So in the first step, you would drink a 50 gram Glucola beverage and you would have your blood drawn to measure your blood sugar one hour later. No fasting is required and it’s only one blood draw. Now, if your blood sugar levels are high, according to different cutoffs for the test, you might be scheduled then for a follow-up diagnostic test on a different day. And about 14 to 23% of people who drink that initial Glucola drink end up needing the second diagnostic test. The second step involves using either a 75 gram or 100 gram glucose drink that you drink fairly quickly. And so this is more glucose than you did in the first step. And it does require that you fast beforehand. So you come in fasting for the test. You have your blood sugar levels drawn fasting. And then you drink the 75 or 100 gram drink. And then your blood is drawn to measure blood sugar at one, two, and three hours after drinking the glucose. So this involves four blood draws with the second step. So neither of these methods is perfect. They both have their pros and cons. So Morgan, can you share with us some of the pros and cons of the one-step and two-step methods?

Dr. Morgan Richardson Cayama – 00:16:23:

Yeah, absolutely. So with that one step method, as Rebecca mentioned, everyone does have to fast or everyone who’s getting screened has to fast or not eat for at least eight hours before that test. And of course, that can be uncomfortable for anyone, but especially for those who are pregnant. And another drawback with this test is that you do have to attend a two hour lab appointment. And that can be difficult for some people in terms of getting to the lab and waiting around for blood draws. So you have really demands on transportation and time as well. Now, the one step method and criteria also result in more people being diagnosed with GDM, which can actually be both a good and a bad thing. So on the one hand, it’s good because that means more people can be identified who might benefit from management and treatment. And these are people who could go on and make lifestyle and nutritional changes to try and reduce their risk of some of those poor outcomes. However, on the other hand, these also mean, like having been diagnosed with Gestational diabetes might also mean higher personal and healthcare costs because you have to more closely monitor your blood sugar levels. You might have to have more medical appointments and meet with a nutritionist, and you might need to pay for testing supplies and medication, especially if you’re somewhere where that wouldn’t be covered by insurance, and you might have more out-of-pocket costs with that. People who are diagnosed with Gestational diabetes might also experience more pressure by their healthcare providers to be induced. And that’s definitely a consideration too. Now with the two-step method, you do not need to fast for that first step, as Rebecca said, and you only need to wait around for about 15 minutes to one hour before you need that blood draw. However, if you do end up needing to do that second step, like if your levels are high enough after the first step, then you need to go on and do the second diagnostic OGTT. You have to come back a different day after fasting overnight, and you do need to drink even more of that glucose, as Rebecca mentioned, so 75 grams or 100 grams, depending on where you are, and wait around for three hours to have your blood drawn. And again, you have those four different blood draws as part of that test. And so while the first screening step in the step two method is much less burdensome compared to that one step method, the second step is a lot more demanding and a lot more involved. And also, I should say that a potential con with both of these methods is that they involve drinking that glucose beverage and Glucola, as you might have heard it called. And some people do experience side effects after they drink this. Again, it’s a lot of glucose or sugar that you’re ingesting in a short amount of time. And so some of these side effects that have been reported in research include bloating, abdominal pain, and nausea. And actually around 8% to 10% of people do experience vomiting, which can interfere with their ability to complete the test. And anxiety and worry around the test is also something that people report. Or even anxiety and worry around having blood drawn, which was a personal issue for me as well. Something that I wasn’t looking forward to when I had my own GDM screening. And one study from 2022 found that 40% of patients who took an OGTT actually did not know why they were even taking the test. They didn’t know what the screening was for. And about half had high levels of anxiety. And so I think this really shows that we can also be doing a lot better about educating people not only around Gestational diabetes. But even why we screen for it, how we screen for it, and what the screening and these tests involve. So as you can see, both methods, again, do have their pros and cons. But we also have some newer evidence comparing actual health outcomes and risks and benefits between these methods. So Rebecca, what does this new evidence suggest?

Dr. Rebecca Dekker – 00:19:55:

Yeah, so in our previous version of the Signature Article, we talked about a Cochrane review that was published in 2017 that attempted to compare the benefits and risks of both methods. However, at that time, there were only a few small studies and the researchers concluded we needed more studies and larger randomized trials on this topic. So now in 2025, we have results from some of these large trials that the researchers were calling for to be done. And overall, I find this really interesting because the global community was really excited about the one-step method and thought, you know, yes, we’re going to diagnose more people, but we’re going to help so many more people and outcomes will be better. In general, the research that has come out in the last five to six years has shown that the one-step method increases the number of people who are diagnosed and treated for GDM, but doesn’t actually improve health outcomes at the population level. So for example, there was one large trial published in 2021 by Hillier et al. This was done in two hospital systems in Hawaii and the Pacific Northwest in the United States. So they included everyone who gave birth at these facilities between 2014 and 2018. And they were able to include everyone because it was standard care. So they didn’t have to get like informed consent from the participants. They just randomly assigned them to get one of the two types of standard care. The one step or the two step. And they ended up with nearly 24,000 participants and 94% of them completed a Gestational diabetes screening, either the one step or the two step method. And as you would expect, rates of GDM were much higher in the one step group, about a 17% rate of GDM compared to 9% in the two step group. And they looked at many different maternal and infant health outcomes. They looked at rates of large babies, gestational high blood pressure, inductions, Cesareans, preterm births, stillbirths, NICU admissions, and much more. And they found no differences between the two groups in any of these outcomes, except there was a slightly higher rate of low blood sugar in newborns in the one step group that was less than 2% higher. So it was statistically different, but it wasn’t like a huge difference. And then in 2024, Gomez et al. published a meta-analysis that combined studies, and they had 15 times the number of participants from that 2017 Cochrane Reviews. This was huge compared to the research we had in 2017. And they combined data from seven different randomized trials, including the trial I just discussed. They found, as we would expect, the one-step method led to more people being diagnosed with GDM, but they did not find higher rates of medication for GDM. They did find that the one-step method resulted in higher rates of NICU admission in newborn low blood sugar, but slightly lower Cesarean rates. And the authors concluded that we need more research on long-term outcomes, like whether or not the one-step or two-step method has any impact on eventual type 2 diabetes diagnoses in the gestational parents and their children. So we go into a lot more detail about these studies and other studies that have come out about diagnosing GDM. So go to the Signature Article ebbirth.com/diagnosinggdm if you want to learn even more about this new area of research. Another area of research that we looked at is screening early in pregnancy for Gestational diabetes. So Morgan, can you highlight for us what we found when we were looking into this research?

Dr. Morgan Richardson Cayama – 00:23:45:

Yeah, so this was a big kind of deep dive that I took when I was looking into the literature because there has been so much new research on this topic. And again, we go a lot more depth and dive into a lot more detail in the Signature Article. But there have been several studies published in the last few years looking at the effectiveness of early GDM screening and treatment. So just as a reminder, most professional organizations recommend screening an early pregnancy for pre-existing type 2 diabetes, not GDM. And type 2 screening is often targeted only in people with those risk factors that Rebecca described earlier. You can learn more about that early screening for type 2 diabetes in the article. But early screening for GDM is screening done well before the usual time-frame of 24 to 28 weeks or that standard of care that we currently practice. And early screening, usually in the research, even happens before 20 weeks. However, this early GDM screening has been complicated by a lack of clear guidelines or cutoff values for what’s considered Gestational diabetes, especially in comparison to that pre-existing type 2 diabetes, and a lack of really effective screening methods in early pregnancy. And we’ll talk a little bit more about why that is too and why screening is just more complicated in pregnancy in general. But in these early GDM screening studies, researchers have been exploring different diagnostic thresholds and cutoffs. They’ve also been exploring different methods like hemoglobin A1C, oral glucose tolerance testing, fasting plasma glucose, or fasting blood sugar levels, for example. So one study found that early hemoglobin A1C testing before 16 to 20 weeks of pregnancy could be really beneficial in helping to roll in and roll out people with Gestational diabetes and go on to help some people avoid having to even ever need a second trimester oral glucose tolerance test. So for example, people with really high hemoglobin A1C levels early in pregnancy could be rolled in as pretty much automatically having Gestational diabetes or receive that diagnosis early and go on and start receiving treatment early. People with really low values, on the other hand, could pretty much be ruled out as not having Gestational diabetes. But anyone with values in between, really low and really high values, would still need to go on and do that second trimester oral glucose tolerance test. So, so far, this research points to some benefits of early screening and treatment. And some researchers who have been doing research in this field believe that we now have enough evidence to recommend it. So, for example, one well-known randomized control trial, it’s called the Treatment of Booking Gestational Diabetes Mellitus or TOBOGD trial. Found that early treatment of GDM before 20 weeks of pregnancy lowered the risk of a poor perinatal composite outcome or a combined outcome. And this is where the researchers looked at things like preterm birth, having a big baby, newborn respiratory distress, stillbirth or newborn death, and a few other poor outcomes for babies. And what they found was that the rate of this outcome was lower among people in the early treatment group at around 25% compared to 31% of people in the control group who did not have early GDM treatment. So they just had the usual standard of care. Their screening 24 to 28 weeks and then received care if needed. However, one of the main reasons for this difference was because the rate of newborn respiratory distress was lower in that early treatment group at around 10% versus 17% in that control or standard of care group. So this was an unexpected finding by the researchers, and they’re not really sure why they saw this, but these researchers still believe that there is enough evidence that as evidence continues to grow on early screening and treatment, that we can begin to recommend early GDM screening and treatment. But this is only one study. There have been other studies, granted they’re typically smaller, the TOBOGD trial, and these studies haven’t found any differences in outcomes between people with early or standard treatment. Some professional organizations, including the American College of Obstetricians and Gynecologists or ACOG here in the U.S., still do not currently recommend early GDM screening just because they don’t feel like there’s yet sufficient evidence on the benefits and harms of diagnosis and treatment before 24 weeks. But this is a rapidly growing area of research. It seems like new studies are published every few months on this topic. So it’s going to be interesting to see how this evolves. And we expect that these professional organizations will continue to monitor that evidence and they may even update those guidelines in the future. So that’s definitely something we want to stay tuned about.

Dr. Rebecca Dekker – 00:28:11:

Yeah, we’ll have to keep our eyes open for new recommendations on the early screening because I think the research is kind of shifting that way. Can we identify people before that 24 to 28 week time point? And I also like that option of perhaps having a hemoglobin A1C, which can be done point of care, by the way. It doesn’t have to be a blood draw. It can be done with finger stick point of care device to see if you can have that earlier in pregnancy and if the results are low enough, you could skip the Glucola drink later in pregnancy. That would be nice. Yeah. So we’ve talked a lot about the oral glucose tolerance test and the infamous Glucola drink that I was just mentioning. And this is still considered the gold standard when you’re screening or diagnosing Gestational diabetes. However, we get many questions from families about whether they have to drink the Glucola. Or if there are any other ways that they can be tested for GDM? And the answer is yes, there are alternative options. And one of the newer options that’s come out since we last updated this article, this is for people who are okay with drinking a glucose drink, but they’re concerned about dyes or artificial ingredients in the standard Glucola beverages. There are now options available without these ingredients. And one that is commonly mentioned to us here at EBB is the Fresh Test. You can learn more by visiting their company website, but on their website, they state that they are labeled as a diagnostic class two medical device by the FDA here in the United States. And so they are considered equivalent to other glucose beverages. So you can order those directly from their website. Or if you want faster shipping, you can order them from Amazon. Although the price does go up quite a bit if you order the fast shipping version, we paid for ourselves. We don’t receive any funding or sponsorships and we don’t get free products here at EBB, but we ourselves went online and ordered a couple of fresh tests to just do taste testing out of curiosity for me and Morgan’s sake. And I ordered them both to be sent to different locations in Kentucky. And one reached Morgan’s place in about a week using the company standard shipping and mine has still not arrived. So if you are interested in this option, make sure you get it well in advance unless your provider stocks it themselves. It’s also worth checking with your provider to see if they are accepting of this drink, but whether I think it’s still a pretty good equivalent to the Glucola drink. We also came across another recent study published out of China that looked at the impact of temperature in adding green tea or soda water to the standard glucose drink. So they looked at eight different combinations. So they had the glucose solution in room temperature or hot or cold. They did glucose at room temperature, hot or cold, but with a green tea bag added to the drink. And they also looked at glucose in room temperature, liquid or cold water mixed with soda water or sparkling water. And the researchers measured people’s perception of taste, side effects, the blood sugar levels and the rates of being diagnosed with Gestational diabetes. And they found that people preferred the taste of the cold solutions or those that included the green tea. And these led to slightly less nausea, but no difference in rates of vomiting. There was also no difference in rates of GDM diagnoses, which is a good thing and means that changing the temperature or adding green tea does not adversely affect the test. However, the glucose in cold soda water or sparkling water did impact participants one hour blood sugar levels. So it was ultimately not recommended by the researchers, but it’s just something good to know that making sure that the drink is really cold or you could add a green tea bag to it to improve the taste. Those are some options. There are a few other alternative methods that people often ask us about, like eating candy or food before testing, home blood sugar monitoring, doing a random fasting glucose test or blood sugar testing and hemoglobin A1C testing. So Morgan, what’s the evidence on these methods?

Dr. Morgan Richardson Cayama – 00:32:44:

Yeah, so we don’t really have time to dive into all of the research and every single study across all of these different alternative methods. But we do present, again, all of that information in a lot more detail in the article, and I am very happy to give the cliff notes. So first, it is important to note that these methods typically do not perform quite as well as the oral glucose tolerance test, especially when it does come to identifying Gestational diabetes later in pregnancy. And so, for example, fasting plasma glucose or blood sugar, it does work really well in diagnosing diabetes in non-pregnant people. But one of the drawbacks with this method is that it doesn’t test your body’s ability to handle glucose after eating. So meaning that it doesn’t challenge your body’s ability to handle that extra load of glucose, which is important for identifying Gestational diabetes during pregnancy. So seeing, you know, after you eat a meal or after you have that extra blood sugar, is your body able to overcome that extra insulin resistance, for example? Now, hemoglobin A1C testing is another common alternative method that we hear about. However, it unfortunately also has its issues, especially later in pregnancy. So this is because hemoglobin A1C levels fluctuate during pregnancy, and these levels can also be impacted by iron deficiency anemia. Now, iron deficiency overall, it’s a pretty common issue during pregnancy, and iron deficiency anemia specifically impacts around 12% of pregnancies here in North America. So that’s another reason why this one is just a little bit harder, a little bit less accurate at diagnosing Gestational diabetes. Now, one thing with the hemoglobin A1C testing, as I talked about earlier, is that it does, again, show promise, especially in early pregnancy, for being able to roll in and roll out people with Gestational diabetes. But again, because those levels fluctuate over pregnancy and because of how they’re impacted by anemia. It just kind of loses its power or it just isn’t as effective later in pregnancy. So that is one drawback with this method. Now, candy and food alternatives, you mentioned, Rebecca, these are pretty popular. And I think we get a lot of questions about these as well as EBB. And actually, Rebecca, I think that you have some personal experience with this method. So can you tell us about that and then maybe more about what the research says with that type of approach?

Dr. Rebecca Dekker – 00:34:59:

Yeah. So I was one of the 10% who vomits and gets really sick after drinking the oral glucose challenge test. So with my first pregnancy, that was a very difficult experience. So the second time around, I still wanted to know if I had Gestational diabetes because I thought it was important. But at the time I didn’t really know a lot of the research. And so I was just trying to figure out, you know, okay, if I just challenge my body and what is the sweetest thing I could eat and then go in for the test. And I don’t recommend this, but I didn’t tell them that I did this. I just said I drank the glucose beverage. And, you know, there wasn’t in a practice where I felt like I could have transparent communication about this, but I did want to challenge myself. And so I found the sweetest thing I could eat, which was a slice of carrot cake with cream cheese frosting. And it had a ton of sugar in it. And I normally don’t eat that much sweets. So I had a large slice. And the funny thing is that I still felt sick afterwards, which I think many of us can identify when you have a large load of glucose. Like if you’re not used to it, your body reacts to it, right? That’s the side effect we’re feeling when we do the glucose challenge. And I only realized later that this is just not equivalent to the glucose test. And I did really well. My blood sugar recovered really quickly. It was at a normal level after, you know, when I got my blood drawn, which I thought was a promising sign, since I just physically couldn’t drink the glucose beverage. But what I didn’t realize at the time is that that is not going to be an equivalent test for those cutoffs that they use, because there is, you know, fat, fiber, other complex carbohydrates in that cake, that then changes how your body digests and metabolizes the sugar in it. So that’s one reason that food or meals are not typically recommended because then the cutoff values aren’t going to work the same. And unfortunately, carrot cake has not been included in any studies that we’ve come across. However, researchers have studied the effectiveness of GDM screening using some candies that have more simple sugars and don’t have like all that added fat and fiber that I had in my carrot cake. So the tests that have been done include candy bars, candy twists, kind of like Twizzlers and jelly beans. And the research studies that we found have shown that people often prefer eating candy over drinking a Glucola beverage, and they typically have fewer side effects. So however, the research on this, there’s just a few older studies on this topic, and most of them are pretty small studies. And they’ve also shown mixed effectiveness in identifying people with GDM. And as I mentioned earlier, one drawback of any food-based GDM screening is that there are different kinds of sugars, and they don’t all have the same effect on your blood glucose levels. So different candies can have fats or proteins or added ingredients that aren’t present in the glucose drinks that can alter your blood sugar results. So this means someone who has true Gestational diabetes might not get a positive result on their GDM screening test if they replace the Glucola drink with some kind of candy. This could result in a missed diagnosis. Also, candy alternatives have only been examined as potential alternatives to the 50-gram two-step glucose screening test, not for a diagnostic test with the 75 grams or 100 grams. So in all of the candy studies, people with positive results still had to follow up with an OGTT to determine whether or not they meet diagnostic criteria for GDM. So another popular alternative that does not involve consuming candy is for someone to monitor their blood sugar at home to get a blood sugar monitoring device to do finger pricks and track them and then discuss their results with their care provider. So one obvious benefit of this home monitoring approach is that you don’t have to drink the glucose beverage and you can do it in the comfort of your own home. But it does require frequent finger sticks and you need access to a device and testing strips. And you have to remember to perform the test throughout the day or for multiple days. Another downside of this method is there’s no clear standard for diagnosing GDM with this method. And it’s also really important that pregnant people follow their normal diet if they’re using this method. So the provider can then provide guidance on whether testing can be stopped, needs to be continued, or if GDM management or treatment is needed. So those are the different options, alternative options for screening and diagnosis. And as we mentioned at the beginning of this podcast, there’s still no single agreed upon approach. So knowing that, can you highlight for us, what some of the different health organizations are recommending so we can kind of see the differences from country to country?

Dr. Morgan Richardson Cayama – 00:40:04:

Yeah, of course. And there are a few, as you mentioned, Rebecca, there tends to be disagreement on that one or two step approach. But yeah, one reason that this topic is so confusing, and I think we get so many questions about it is because the guidelines do vary. Depending on which country and which professional organization you refer to or whose recommendations that you’re looking at. So here in the United States, the American College of Obstetricians and Gynecologists or ACOG does recommend that two step approach with an oral glucose tolerance test. In step one, again, they recommend all pregnant people be screened for Gestational diabetes. Using the 50 gram one-hour OGTT between 24 to 28 weeks of pregnancy. People who have those high blood sugar levels, depending on the criteria used by the provider or the hospital, then go on to do that step two, which again is that 100 gram, three hour OGTT. So again, ACOG does not currently recommend early screening for GDM. They do recommend early screening for pre-gestational type 2 diabetes in people with risk factors. So in Canada, the Society of Obstetricians and Gynecologists, they also recommend a universal two-step approach similar to ACOG, where everyone who is pregnant completes a 50-gram, one-hour OGTT, again, between 24 and 28 weeks. Now their step two diagnostic test is a 75 gram two hour OGTT. So that’s a little bit of a variation from us here in the U.S. and with ACOG. But they also state that the one-step approach is acceptable. It’s not the preferred, but it’s acceptable. And like ACOG, they currently do not recommend early GDM screening, but do recommend screening for type 2 diabetes early in pregnancy for people with risk factors. Now in the UK, the National Institute for Health and Care Excellence, or NICE, they recommend a targeted approach, meaning only people with risk factors are even screened for GDM. So they recommend using a one-step approach with a 75-gram two-hour OGTT between 24 and 28 weeks of pregnancy. However, if you’ve been previously diagnosed with GDM, they recommend either self-monitoring or the one-step 75-gram OGTT at the first prenatal appointment. And then a second test between 24 to 28 weeks if needed. If their levels are normal, if your levels are normal during that first step, you would still get a second screening at 24 to 28 weeks just to double check. So hopefully that provides a little bit of clarity for folks. We do have a convenient table in the Signature Article that lays out all of these different recommendations across some of the different professional organizations around the world. And I’m a visual person. So I think. That is a lot more helpful for me to kind of see how these different organizations and even some that I didn’t mention here follow Gestational diabetes screening and diagnostic recommendations. And so aside from these, there are also people who are just not interested in being screened for Gestational diabetes. And so Rebecca, what if I want to decline the gestational diabetes test and what are the risks? What are some risks that I might face if I don’t want to be screened at all?

Dr. Rebecca Dekker – 00:43:07:

Yeah, so first the disclaimer for me is that having a test for GDM is considered evidence-based care because there are substantial risks to your health and your baby’s health if you have abnormally high blood sugar levels and they’re not identified and treated during pregnancy. But one of the interesting updates to this version of the Signature Article is we did find a study published earlier this year in 2025 by Nethery et al. They looked at health outcomes among pregnant people who chose not to screen for GDM, which they refer to as screening non-adherence. I think this is fascinating because we’ve never had a study on this before. So this study was carried out in British Columbia, Canada, and it looked at all births where the birthing person gave birth to only one baby between 2006 and 2019 and whose care was led by a midwife. They did this because declining to be screened for GDM is more common in pregnancies with midwifery-led care. It’s more likely to be because the pregnant person chose to decline the test rather than an issue with access to screenings. It’s not because they have less access to care or prenatal care in general, but because it was their choice. And the researchers looked at a range of health outcomes, like was your baby large for gestational age or small for gestational age? Did your baby have low APGAR scores at birth? Were there higher rates of preterm birth, NICU admission, Cesarean, perineal tears, and stillbirth? In their analysis, the researchers controlled for other factors that can impact these health outcomes, so they took into account things like age, smoking, BMI, and other risk factors for poor health outcomes. They were able to include about 83,500 pregnancies, and then they categorized the pregnancies based on screening status, including those who completed standard OGTT screening between 24 to 28 weeks, those who did non-standard screenings like getting the hemoglobin A1C or doing random blood tests to check for blood sugar, and those who did not screen or do any testing at all. So they had about 18,000 participants who did not screen at all. And when they compared them to those who completed routine screening and had normal blood sugar levels, which was around 58,000 people, they found that those who did not screen had a lower risk of large for gestational age babies and Cesarean, but they had a higher risk of stillbirth and a higher risk of small for gestational age babies. They didn’t see any differences in any of the other outcomes between these two groups, again, comparing those who declined screening and those who did the screening but had normal blood sugar levels. Researchers also wanted to see if there were differences in outcomes between people with and without pre-pregnancy risk factors for GDM in the non-testing group, so targeting like a higher risk group of people who declined to be tested for GDM. And they found, unfortunately, an even higher risk of stillbirth in those with risk factors who declined to be tested for GDM. Their risk of stillbirth was two and a half times higher. However, the researchers noted there is a possibility that people who declined GDM screening might have also declined other interventions like screenings for fetal anomalies, or they could have declined other health treatments that could have increased their risk for stillbirth. And the researchers noted that, quote, are finding strongly support screening for those with pre-pregnancy GDM risk factors, end quote. Here at EBB, we do want to remind you that it is a human right to decline medical treatment unless you are found formally to be incapable of making medical decisions. And in the United States, at least, ACOG has affirmed that mothers with GDM have the right to individualized care and the right to refuse care. So we have another interesting question. It would be, I thought it would be interesting to kind of end with, and it’s come up a few times now. It keeps getting sent to us by email and on Instagram, and we addressed it in our Signature Article update. And this question revolves around the role that sperm plays in the formation of a pregnancy and the risk of GDM. So Morgan, what did you find when you looked into this?

Dr. Morgan Richardson Cayama – 00:47:47:

Yes, I love this question because I also had friends that have asked me this or have sent me research on this. It’s really interesting. And the short answer is, unfortunately, we cannot say for sure whether the sperm used to fertilize the egg causes GDM. That causal relationship, again, we can’t 100% say that that is the case. However, the suspected link between sperm and GDM has to do with the sperm’s role in the development of the placenta and the placenta’s role in the risk for GDM. And I just want to say, too, there are many genetic and environmental factors that impact someone’s risk of developing Gestational diabetes. Hormones do appear to play a large part in the development of the placenta. And the hormones released by the placenta are what contributes to that insulin resistance. So we know hormones are one part of this equation as well. And researchers have been exploring the ways that epigenetic factors from the male biological parent or from the sperm donor in the case of an assisted sperm donor pregnancy influence the health of the baby and the development of the placenta. And so epigenetics has to do with behaviors and factors in the environment that cause changes that affect the expression of genes. And these can be impacted by things like the person’s health, your health or your age, for example, and even environmental exposures like substance use or if you’ve been exposed to food insecurity or even exposure to trauma. And studies have shown that these factors specifically can impact epigenetic changes in the DNA in the sperm. And that the sperm, again, plays a role in the development of the placenta. So this is all kind of related and associated, all of these factors. But we really need more research to fully understand the ways that the sperm and the placenta and GDM are connected. And we do link to some of these recent research articles and resources where you can learn more about these connections in the Signature Article. So it’ll be interesting, too, to kind of follow this research and see how it progresses and what people say ends up kind of being that connection and that big picture between sperm and the risk of GDM.

Dr. Rebecca Dekker – 00:49:54:

That’s such an interesting question. Just raises so many questions in my mind about the risk for preeclampsia, because that’s also related to the placenta or gestational hypertension. And then, you know, what about preconception health of the male biological parent? And what role does that play? So I think it’s going to be an interesting area to watch the research evolve. And maybe next time we update this article, we’ll know even more. So before we wrap up, I’d love to know, Morgan, what was something that you learned or surprised you while you were researching this topic? So you mentioned to me, you know, this was a new area of research for you to dive into. We have spent like half a year reading the research on this together. And, you know, what’s one of your surprise takeaways?

Dr. Morgan Richardson Cayama – 00:50:39:

Yeah, well, in addition to the sperm’s role, which again, I’m very fascinated by, I really wasn’t all of that familiar with the range of alternative methods. This was not really something that I had explored before. I had just sort of accepted my fate of having to drink the glucose drink, even though knowing from, you know, friends that it wasn’t the most enjoyable thing during pregnancy. But for me, like I had mentioned earlier, I was a lot more concerned and had a lot more anxiety around the blood draws associated with the test and just blood draws in general throughout pregnancy. That was what kind of gave me the most sort of fear. But yeah, just knowing that there’s all of these alternative methods, especially if you are someone who experiences a lot of nausea or vomiting with the test, or if that’s one of your fears, I think that there’s a lot of different promising methods that you can talk about with your provider and see what might be right for you. So that was something that was cool for me to learn about.

Dr. Rebecca Dekker – 00:51:29:

Yeah, and I’m really interested to see if the early testing using the hemoglobin A1C finger prick evolves into something that becomes more available. I know in the research we reviewed, they talked about its usefulness in parts of the world where you don’t have access to laboratories and you can’t have blood draws and how that might be really helpful in identifying people early who are at high risk for GDM. And then for me personally, I was most surprised by all of this new research really showing no clear benefits of the one-step method over the two-step method. For a long time, it felt like in the U.S., we were kind of behind the times using the two-step method. And I think the reason we still did is the organizations here wanted to be conservative. They’re like, this is going to double the number of people diagnosed with GDM. Our healthcare system can’t really support that. And we don’t know if there’s actual benefits to doing that. And it’s interesting to see that now there’s research kind of supporting that approach is okay. And I’m curious to see how that research will evolve over the next five years. So. That was kind of my big takeaway. So as we wrap up, what is the bottom line on diagnosing GDM? So GDM is diabetes that begins during pregnancy, but we also have to be aware that some people enter pregnancy with undiagnosed pre-existing type 2 diabetes. And for this reason, you might see providers offering diabetes screening early in pregnancy if you have risk factors. Most organizations around the world still agree that GDM screening should take place between 24 to 28 weeks of pregnancy, but there is still disagreement on the best way to do this. So in the U.S. and Canada, the two-step method is commonly used. Most other countries around the world prefer the one-step method. Both of these methods involve the use of oral glucose tolerance tests, often with the Glucola drink. There are alternatives to drinking the standard glucose solution. So if you’d rather not drink the standard glucose beverage or you can’t due to vomiting or other side effects, you can talk about alternative methods with your provider. However, we don’t have sufficient evidence to state which alternative best or how accurate these alternatives may be. We do, though, have strong evidence that treating GDM improves birth outcomes for both birthing people and their babies, and screening for GDM is considered evidence-based care. It’s also important that we shift how we talk and think about being diagnosed with Gestational diabetes. Most of the time, when you hear someone describe their results, they’ll say, I failed the GDM test or I had a failed screening. This is really stressful and can require lifestyle changes or management and treatment that can be demanding or costly. I really would prefer that we stop using the word fail and instead talk about testing positive for GDM or the screening test was positive and I have to go on to do the diagnostic test. So just because if you do the two-step method, just because that first step was positive doesn’t mean you are going to have a diagnosis of GDM. And the benefits of positive tests are that you can uncover potential health problems before they progress and adversely affect your birth outcomes and the health of you and your baby. So a positive diagnosis can be a real opportunity to make some small shifts in your lifestyle or large shifts if needed that can positively impact the future health of both you and your child. 

So we covered a lot of information today on diagnosing Gestational diabetes and there’s even more info in this article that we didn’t have time to cover on the podcast. You can find everything in the newly updated Signature Article, Evidence on Diagnosing Gestational Diabetes on our website at ebbirth.com/diagnosinggdm, along with an updated two-page handout in both English and Spanish. We’ll also link in the show notes to our article on Inducing Labor for Gestational Diabetes, a related article all about big babies. And then one of our favorite resources for Gestational diabetes is a book called Real Food for Gestational Diabetes by Lily Nichols. He’s a registered dietitian, nutritionist, and certified diabetes educator. Her books, especially the Real Food for Gestational Diabetes one for this topic, it’s evidence-based and includes citations to research articles, and it can be really helpful if you have that positive test. So thanks again for joining us everyone today on this really important episode. I hope you found it helpful and we look forward to talking with you again soon. Bye everyone. Today’s podcast was brought to you by the Signature Articles at Evidence Based Birth®. Did you know that we have more than 20 peer-reviewed articles summarizing the evidence on childbirth topics available for free at evidencebasedbirth.com? It takes six to nine months on average for our research team to write an article from start to finish. And we then make those articles freely available to the public on our blog. Check out our topics ranging from advanced maternal age to circumcision, due dates, big babies, Pitocin, vitamin K, and more. Our mission is to get research evidence on childbirth into the hands of families and communities around the world. Just go to evidencebasedbirth.com, click on blog. And click on the filter to look at just the EBB Signature Articles.

When we think of screening for diabetes during pregnancy, we often think of screening for GDM. However, it’s also recommended that doctors screen early in pregnancy for overt (or pre-existing/pregestational) Type 2 DM in those with risk factors. There isn’t an agreed upon or recommended method for screening for overt Type 2 DM in pregnancy, or for diagnostic criteria specific to pregnancy (to read more about screening guidelines, see the section “What do Professional Guidelines say about Screening for GDM”). So, a group of researchers in the U.S. conducted a study to look at what methods were most used by doctors doing Type 2 screenings in the first trimester of pregnancy (Wilkie et al. 2023).

In this study, researchers looked at a combination of Hemoglobin A1c (HbA1c), oral glucose tolerance testing (OGTT), and fasting plasma glucose (FPG) methods. They also compared pregnancy and maternal health outcomes between those who were screened early for overt diabetes, and those who did not receive any GDM screening until 24-28 weeks. The health outcomes included rates of Cesarean, preterm birth, gestational hypertension, preeclampsia, elevated liver enzymes and low platelets (HELLP) syndrome, and GDM.

The researchers looked at U.S. medical claims data from a national database to find pregnant people who were screened for diabetes in the first trimester (before 14 weeks of pregnancy). The database included people with employer-based commercial insurance and Medicare Part D plans, who gave birth from January 2016 to December 2018 and were between 15-44 years old. They excluded people who had a molar pregnancy, ectopic pregnancy, or who were previously diagnosed with pre-existing diabetes (Type 1 or Type 2). Out of a total of 328,615 people, they identified 71,973 (18%) who were screened for diabetes early in pregnancy.

The most common types of early screening were the HbA1c (53%) followed by FPG (30%) and OGTT (17%). Those screened in the first trimester were more likely to be older, have bigger bodies, have a prior history of GDM, have chronic hypertension or high lipids, and have a family history of diabetes. This finding makes sense, because early screening is already recommended for people with risk factors. They also found that people who were screened in the first trimester had higher rates of poor health outcomes regardless of whether they screened positive for diabetes. The researchers think this is because these people were more likely to be high-risk in the first place.

In 2021, Hillier et al. published a randomized trial comparing the one-step method (75-gram OGTT) with the two-step method (50-gram OGTT followed by a 100-gram OGTT if needed). They were interested in how these methods impact the rate of GDM diagnoses and health outcomes.

This study was a large, “pragmatic” randomized trial that took place at two Kaiser Permanente locations in Hawaii and the Pacific Northwest in the U.S. In a pragmatic trial, researchers try to follow real-world conditions so that the results can hopefully be applicable to regular hospital settings. All patients who gave birth at these hospital systems from 2014 to 2018 were included in the study.

Because this was a pragmatic trial, patients and providers were not “blinded” to study groups — meaning they would know whether they had been assigned to the one-step or two-step method. However, patients and providers were not shown data reports, so they did not know how the study was progressing. Patients were excluded from the study if they had a miscarriage or pregnancy termination, if they were pregnant with multiple babies, were less than 18 years of age, or had prior bariatric surgery.

Informed consent was waived in this study, because both treatments (one-step and two-step) were considered standard care.  However, if the provider or patient did not agree with the group assignment, they could refuse to adhere to the assigned group. For example, if a patient in the one-step group had transportation problems, their provider might ignore instructions to do the one-step method and instead use the two-step method. This way, a non-fasting test could be performed during a regular prenatal visit.

A total of 23,792 pregnant participants took part in this study, and 94% of them completed a screening process for GDM. Of those who were randomly assigned to receive the one-step screening, 66% adhered to their assigned group. Of those who were assigned to receive two-step screening, 92% adhered to their assignment.

As would be expected, rates of GDM were higher in the one-step group (16.5% vs. 8.5%). However, identifying and treating more people with GDM did not go on to improve health outcomes. There were no differences between groups in rates of large for gestational age babies, gestational hypertension or preeclampsia, or needing a first-time Cesarean. There were also no differences between the two groups in a perinatal composite outcome (or combined outcome), which included any of the following for babies: stillbirth, newborn death, shoulder dystocia, bone fracture, or any arm or hand nerve damage from a birth injury. Rates of shoulder dystocia were approximately 2% in both groups.

The researchers also looked at a number of other health outcomes, such as jaundice, sepsis, NICU admission, preterm birth, needing an induction of labor, and more. There were no differences between groups, except there was a higher rate of newborn low blood sugar (hypoglycemia) in the one-step group (9.2% vs. 7.5% in the two-step group).

In 2021, Davis et al. published a randomized trial comparing the 75-gram OGTT with IADPSG criteria vs. the 100-gram OGTT with Carpenter-Coustan criteria. This study, which enrolled 921 pregnant participants, took place between 2015 and 2019 at a single hospital in the U.S.

Before randomizing the participants, the researchers first gave everyone a non-fasting, 50-gram OGTT. If the blood glucose levels were 200 or greater, then they were considered to have known GDM and were excluded from the rest of the study. For everyone else, if blood sugar levels were less than 200, then they were randomly assigned to take either the 75-gram OGTT with IADPSG criteria, or a 100-gram OGTT with Carpenter-Coustan criteria. Health care providers were blinded to the criteria used to diagnose GDM. Everyone who tested for positive received standard care for GDM.

The primary outcome the researchers looked at was large-for-gestational age birth weight (≥90% for sex and gestational age). Secondary outcomes included things like Cesarean birth, macrosomia (big baby), and maternal morbidities (e.g., 3rd or 4th degree tears, postpartum hemorrhage). They also looked at a composite newborn outcome (combined outcome) that included hypoglycemia (low blood sugar), hyperbilirubinemia requiring phototherapy (jaundice), stillbirth, and birth trauma that included shoulder dystocia or brachial plexus injury.

Researchers found that rates of GDM diagnoses were much higher in the IADPSG group (14.4% vs. 4.5%). However, there were no differences in rates of large-for-gestational age birth weight between groups. There were also no differences in Cesarean rates or other maternal or infant health outcomes.

However, rates of the composite newborn outcome were higher in the IADPSG group (18.8% vs. 15.6%). This was mainly because there were higher rates of newborn low blood sugar in the IADPSG group.  

The IADPSG group also reported fewer testing side effects (nausea, vomiting, dizziness, hypoglycemia), but ended up needing more antenatal tests during pregnancy and were prescribed more diabetes medications.

The researchers concluded that the IADPSG criteria resulted in more pregnant people diagnosed and treated for gestational diabetes, without lowering rates of large-for-gestational age babies or maternal or newborn illness. However, due to this study’s small sample size, only 10% of the participants ended up being diagnosed with GDM. The authors estimate that you would need about 10,000 participants in a study of this type to truly examine the impact of the diagnosis method on infant birth weight.

In 2023, Ramezani Tehrani et al. published a large, randomized controlled trial that took place in Iran. They randomly assigned 28,711 participants to second trimester testing with either the one-step or two-step method. This was the first large trial comparing these two methods in a low- or middle-income country.

Patients were diagnosed with GDM if they surpassed one cut-off on the 75-gram one-step test, or if they surpassed two cut-off values on the 100-gram test. All patients who were diagnosed with GDM received standard care.

The researchers found that rates of GDM diagnoses were higher in the one-step group (9.3% vs. 5.4%). However, there were no differences in any pregnancy, birth, or newborn health outcomes, including no differences in rates of large-for-gestational age birth weight, primary Cesarean, preterm birth, newborn low blood sugar, jaundice, preeclampsia, NICU admission, birth trauma, or low birth weight. They concluded that the one-step method increased the number of pregnant people who were diagnosed with GDM and received treatment for this condition, without improving health outcomes.

In 2024, Gomes et al. published a meta-analysis that had 15 times the number of participants compared to the 2017 Cochrane review. They included the three trials discussed above, plus four smaller studies from Turkey, India, and the U.S.

When all the data from these studies were combined, the researchers found that the one-step method led to higher rates of GDM, but not to higher rates of medication use for GDM. There was no difference between the one-step method and two-step method in rates of large-for-gestational age infants. However, the one-step method resulted in higher rates of NICU admissions and newborn low blood sugar, and slightly lower overall Cesarean rates.

One theme you might have noticed is that researchers consistently seem to find that the one-step method leads to higher rates of temporary low blood sugar among newborns. Gomes et al. explain that this might be because more infants in the one-step group are screened for hypoglycemia– as this is standard practice with GDM. So, more GDM diagnoses results in more screening (and more identifying) low blood sugar in newborns born to parents who received one-step testing.

Gomes et al. concluded that we need more research studies that measure long-term outcomes. Up to this point, researchers have only looked at the short-term birth outcomes of one-step vs. two-step screening. For example, we do not know if identifying and treating more people with GDM using the one-step method has any impact on rates of eventual Type 2 DM diagnoses among participants or their offspring.

A small trial from Mexico (2003) found that pregnant people who received 50 grams of glucose in their food, rather than as a drink, reported far fewer overall side effects (7% versus 80%). However, eating food as a test has drawbacks, which we discuss further in the “Evidence on Alternative Methods” section.

Another trial from the U.S. (1992) compared people who received two different kinds of 50-gram glucose drinks (monomer versus polymer). The glucola drink widely available in the U.S. is usually a monomer glucose drink. More pregnant people developed symptoms after the monomer drink than the polymer drink (51% versus 27%).

Another trial from the U.S. (1994) compared people who received a candy bar versus two different kinds of 50-gram glucose drinks, a monomer and a polymer. Pregnant people preferred the taste of the candy bar, but about half of the people in the candy bar group still reported one or more side effects—the same frequency of side effects as with the monomer glucose drink. Of the three types of glucose screening tests, the fewest side effects were reported after the polymer glucose drink (9%). We do not have any evidence from randomized controlled trials on whether the polymer glucose solution results in fewer or more diagnoses of GDM compared to the monomer glucose solution, which is more common and considered the standard.

A large observational study from the United Arab Emirates followed more than 5,000 pregnant people who took the 3-hour, 100-gram OGTT (Agarwal et al., 2004). They found that 503 participants (9.8%) were not able to finish the test due to side effects. Vomiting was the most common reason for not being able to complete the test, experienced by more than 8% of people in the study.

Another observational study carried out in 2022 found that 40% of patients who took a 75-gram OGTT did not know why they were taking the test, and 48% had high levels of anxiety during the test. However, most (90%) would recommend the test to their friends (Alecrim et al. 2022).

A randomized clinical trial was recently conducted in China that looked at the impact of temperature and additives in OGTT on people’s perceptions of taste, their experiences of side effects, their blood sugar levels, and diagnosis of GDM (Wang et al. 2023). Their study looked at 8 different combinations of glucose solution: 1) glucose in room temperature water; 2) glucose in hot water; 3) glucose in cold water; 4) glucose in hot water with a green tea bag; 5) glucose in room temperature water with a green tea bag; 6) glucose in cold water with green tea bag; 7) glucose in room temperature soda water; and 8) glucose in cold soda water.

Overall, they found that people preferred the taste of the cold solutions or those that included green tea, and that these led to slightly less nausea. None of the solutions had an impact on GDM diagnosis, participants’ satisfaction, vomiting, headache, or bloating. However, the glucose in cold soda water did impact participants’ 1-hour blood sugar levels, so it was not recommended by researchers.

A study using data from the U.K. found that random plasma glucose (RPG) testing at booking, or at the first prenatal visit around 12 weeks of pregnancy, performs fairly well at identifying hyperglycemia in high-risk pregnant people (Meek et al. 2020).

This study included data from a few different studies in the U.K. to look at the effectiveness of different high blood sugar screening methods (RPG, HbA1c, FPG). At the time of the study, the researchers were exploring alternative screening options that could be used during the COVID-19 pandemic to identify people at the highest risk of hyperglycemia who would need blood sugar management. In the U.K., early screening with HbA1c or RPG is typically recommended at the first prenatal visit for those with risk factors.

The researchers included one study (with 17,736 people) in their paper that compared results from early RPG screening to later GDM screening. Study participants, all of whom were pregnant with their first baby, were offered an RPG around 12 weeks of pregnancy, followed by a 50-gram screening OGTT at 24 weeks and, if needed, a 75-gram diagnostic OGTT at 28 weeks.

The researchers found that RPG test results at 12 weeks were correlated with later GDM results. They also found that for early RPG testing to identify a similar proportion of people with GDM as they see in the broader U.K. population (~5%), the cutoff value for the test would need to be ≥8.5 mmol/L (153 mg/dL). Overall, the sensitivity of the RPG testing was low (42%), but the specificity was high (96%). You can learn more about sensitivity and specificity in the “Evidence on Alternative Methods” section below.

The researchers concluded that despite its low sensitivity, RPG testing could still be useful for targeted testing in high-risk people, especially in places or situations where the OGTT isn’t available.

A high-quality study found that early HbA1c screening could lower the number of pregnant people who need second trimester OGTTs by more than half (Saravanan et al. 2024).

This study, which took place in India, Kenya, and the U.K., looked at the effects of early HbA1c testing before 16-20 weeks of pregnancy. The purpose of the study was to test how well an early HbA1c test by itself or an early HbA1c test plus a risk score (that includes age, BMI, and family history of diabetes) can identify people who will eventually test positive for GDM with a 75-gram diagnostic OGTT at 24-28 weeks. HbA1c was measured with both blood draws and point-of-care finger pricks. The researchers followed participants to see if these methods for early screening could lower the number of people who needed an OGTT later in pregnancy.

Data were collected between February 2016 and December 2019 from seven centers in India (3,070 participants), seven centers in Kenya (4,104 participants), and a cohort of people who were recruited for another study from ten centers in the U.K. (4,320 participants). Study participants were between 18-50 years old and less than 20 weeks pregnant (Kenya) or less than 16 weeks pregnant (India and the U.K.). People were excluded from the study if they had Type 1 or Type 2 diabetes; were on metformin for up to 6 weeks before recruitment for anovulation (not having a period), irregular periods, or infertility; or had severe anemia, anormal hemoglobin or other blood disorders, or any other serious medical conditions.

This study used 2010 IADPSG and 2013 WHO guidelines to diagnose GDM, and a total of 1,037 people (407 in India, 65 in Kenya, 565 in the U.K.) were diagnosed. The researchers found that the use of HbA1c by itself (without the other risk factors) could lower the number of people needing second trimester OGTTs by about half (42-50%).

However, the results of the HbA1c test when combined with the risk factors was more accurate at identifying people who later tested positive for GDM at 24-28 weeks. The researchers estimated that this approach could lower the number of people who need second trimester OGTTs by even more (50-64%).

Overall, the researchers concluded that early pregnancy HbA1c (with or without factoring in other risk factors) correctly identified about 50% of people who were diagnosed with GDM between 24-28 weeks. The researchers also found that point-of-care finger pricks worked about as well as the blood draw at identifying people with GDM, meaning no blood draws were necessary! This method could be especially useful in remote areas or places with no access to laboratories.

What do these results mean? Well, this study showed that early HbA1c testing worked well at “ruling in” and “ruling out” GDM. People who are “ruled in” based on their early HbA1c results can be treated immediately for GDM and don’t need a later OGTT. People who are “ruled out” and at lowest risk also could skip the OGTT later in pregnancy. For everyone else (with in between scores), an OGTT would still be recommended in the second trimester.

Something important to note about this study is that the researchers used different cut-off scores in different countries, because the different populations had different test results. For example, in Kenya, an early HbA1c score of 5.2% or less (a result that had 80% sensitivity for detecting GDM) could be used to “rule-out” GDM, meaning that these pregnant people could potentially skip the OGTT at 24-28 weeks. Meanwhile, an HbA1c score of 6.0% or higher (a result that had specificity of 97%) could be used to “rule-in” GDM and these people could go ahead and start treatment. Everyone with scores in between would still need the OGTT at 24-28 weeks.

However, in the U.K., the “rule-out” score (5.2%) and sensitivity (80%) were the same, but the “rule-in” score was 5.6%, and its specificity was 91%. So, different cut-offs might be needed in different populations.

In a randomized trial, researchers found that immediate treatment of GDM (before 20 weeks of pregnancy) lowered the risk of a combined outcome of adverse health results (Simmons et al. 2023).

The aim of the Treatment of Booking Gestational Diabetes Mellitus (TOBOGM) trial was to see whether treating GDM before 20 weeks of pregnancy improved health outcomes for the birthing person and baby (Simmons et al. 2023). Data from this study were collected between May 2017 and March 2022 from 17 hospitals in Australia, Austria, India, and Sweden.

Study participants had to be at least 18 years old and pregnant with a single baby. They also had to have at least one risk factor for high blood sugar, such as being previously diagnosed with GDM, having a bigger body, or being 40 years old or older. All participants completed a 2-hour 75-gram OGTT before 20 weeks of pregnancy, and on average this first test was done around 15 weeks and 6 days of pregnancy.

They excluded participants who already had diabetes or who had very high glucose results on this test, because this was considered overt Type 2 DM and required immediate treatment. Participants who screened positive for early GDM were randomly assigned to either receive treatment right away (the immediate treatment group), or to wait until after the traditional 24-to-28-week second trimester GDM test results, depending on whether they screened positive for GDM (the control group included deferred or no treatment). A total of 793 people were included in the study – 406 who were assigned to be treated immediately and 396 who were assigned to the control group. The people in the control group received a repeat OGTT at 24-28 weeks, and 67% ended up screening positive again for GDM and began receiving treatment.

The primary research outcome in the study was a composite (or combined outcome) of poor perinatal outcomes that included preterm birth, birth trauma, having a big baby, newborn respiratory distress, needing phototherapy for jaundice, shoulder dystocia, and stillbirth or newborn death. They also looked at other outcomes like rates of Cesarean, labor induction, and perineal tears.

They found that immediate treatment of GDM before 20 weeks lowered the risk of the primary composite outcome (24.9% in the immediate treatment group versus 30.5% in the control group). The main reason for this difference was because the rate of newborn respiratory distress was lower in the immediate treatment group (9.8% versus 17.0% in the control group). The rates of other health issues in the composite outcome were similar between the two groups. This reduction in the primary outcome was also greater for participants who had higher glucose levels at the time of the first test and for those whose first test was before 14 weeks of pregnancy compared to after 14 weeks. When looking at other health outcomes, the researchers found lower rates of perineal (3rd and 4th degree) tears and higher rates of breastfeeding initiation in the immediate treatment group.

However, the researchers also found that early treatment of GDM for people with lower glucose values (who still tested positive for GDM but were on the lower end of the spectrum) had a higher risk of having small-for-gestational age babies (12.0% in the immediate treatment group versus 9.2% in the control group).

The researchers also conducted another analysis of data from this study (Simmons et al. 2024). The purpose of this secondary analysis was to compare perinatal outcomes between three groups of participants:

• Participants who had “early” GDM (before 20 weeks) but didn’t receive treatment until 24-28 weeks (if their GDM was still present) (254 people).
• Participants who did not have early GDM but who were diagnosed with “late” GDM between 24-28 weeks and treated (467 people).
• Participants who did not have early GDM and whose blood sugar levels were also normal during their 24-28 week GDM screening (2,339 people).

The primary outcome in this analysis was the same composite outcome that the researchers used in the TOBOGM study described at the beginning of this section. When comparing groups, the researchers took into account any factors that might impact the risk of these outcomes, like the birthing person’s age, ethnicity, BMI, smoking status, number of prior pregnancies, and level of education. They were able to “control” for these factors in their final analysis, to try and isolate the effect of the timing and treatment of GDM diagnoses.

They found that people with early GDM who did not receive early treatment were more likely to experience a poor perinatal composite outcome compared to people with late GDM or people with normal blood sugar levels. People in the early GDM group also had bigger babies, higher rates of preterm birth, and more babies with jaundice. However, people in both GDM groups (early or late) were more likely to be induced, have a newborn with respiratory distress, have a newborn needing phototherapy and have a newborn admitted to the NICU compared to people who had normal blood sugar levels in pregnancy. There were no differences between groups in rates of high blood pressure or Cesarean birth.

Because rates of the composite outcome were higher for people with early GDM who did not receive routine treatment until 24-28 weeks, these researchers concluded that early treatment is important and should be included in professional guidelines.

Researchers carried out a randomized trial to determine whether early GDM screening with an OGTT between 14-20 weeks of pregnancy led to better health outcomes than routine screening between 24-28 weeks (Harper et al. 2020). This trial was unique in that it only included pregnant people with bigger bodies.

Data for this study were collected between 2013 and 2018 at the University of Alabama Birmingham and Ochsner Medical Center in New Orleans, Louisiana. Participants had to begin receiving prenatal care before 20 weeks of pregnancy and had to have a BMI  ≥ 30 kg/m2. People were excluded from this study if they had a prior Cesarean, were previously diagnosed with diabetes, or had bariatric surgery, a major medical illness, fetal anomalies, or chronic steroid use. All participants had an HbA1c test between 14-20 weeks to screen for overt Type 2 DM and received treatment if needed.

Participants were randomly assigned to either early OGTT screening between 14-20 weeks of pregnancy (459 people) or routine OGTT screening between 24-28 weeks (463 people). Participants in both groups had similar characteristics such as age, BMI, and race. GDM screening in this study was done using the standard 2-step method (1-hour, 50-gram OGTT followed by a fasting, 3-hour, 100-gram OGTT if needed). Carpenter and Coustan criteria were used to diagnose GDM. People who were assigned to the early screening group but were negative for GDM were re-screened between 24-28 weeks. People in the early screening group were diagnosed with GDM on average around 24 weeks, while the routine screening group was diagnosed on average at 27 weeks.

After a GDM diagnosis, participants received standard GDM care based on the policies at their medical center. Standard care included education on diabetes and how to self-monitor blood sugar levels. If more than half of someone’s self-monitoring levels were high, they were prescribed medication.

The primary outcome for this study was a composite of outcomes (combined outcome) that included having a big baby, Cesarean, pregnancy-induced hypertension (gestational hypertension, preeclampsia, or eclampsia), shoulder dystocia, newborn hypoglycemia (low blood sugar) or newborn hyperbilirubinemia (jaundice).

The researchers compared outcomes between all people in both screening groups and between only those diagnosed with GDM in both groups. They did not find a difference between groups in the rates of primary composite outcome (approximately 51-57% overall). They also did not find a difference between groups when they looked at rates of health issues. However, participants in the early screening group were more likely to receive insulin (2.4% versus 0.7%). Participants diagnosed with GDM in the early screening group also gave birth earlier (36.7 weeks versus 38.7 weeks).

One limitation with this study was that it was also not “blinded,” meaning that doctors and participants knew which group someone was assigned to. The researchers think that this led to doctors prescribing more insulin in the early screening group and recommending earlier births for those diagnosed with GDM. Overall, the timing of GDM diagnosis was only 3 weeks earlier for the early diagnosis group. It’s possible that if screening and treatment took place even earlier, we might have seen different results.

In 2019, researchers published a randomized trial that examined whether treating high blood sugar earlier in pregnancy led to better health outcomes for babies and birthing people (Roeder et al. 2019).

Data for this study were collected between 2013 and 2016 at the University of California San Diego (UCSD). At this center, all pregnant patients had a standard first trimester blood draw for HbA1c and FPG testing. Patients with HbA1c values ≥5.7% or FPG ≥92 mg/dL were referred to a diabetes and pregnancy program, where participants were recruited for this study. Study participants had to be at least 18 years old, be pregnant with a single baby, be receiving care and planning to give birth at UCSD, and have high blood sugar defined as HbA1c 5.7%-6.4% and/or FPG 92-125 mg/dL. People were excluded from this study if they had pre-existing diabetes or were diagnosed with overt Type 2 DM in the first trimester, or if they had their HbA1c and FPG blood draw too late (after 15 weeks of pregnancy).

Participants were then randomly assigned to either receive treatment for GDM immediately (82 people) or wait until 28 weeks (75 people). Treatment for both groups was identical and included meeting with certified diabetic educators to learn about dietary changes, exercise, and using a glucometer to monitor their blood sugar levels. If more than 40% of their blood sugar levels were abnormally high after 2 weeks of diet and exercise, then participants began medication.

The main outcome in this study was umbilical cord blood C-peptide results greater than the 90th percentile, checked at the time of birth. This lab result can be used as a marker for high levels of insulin, which is associated with children being more likely to develop insulin resistance and/or Type 2 DM later on. The researchers also looked at other outcomes like birth weight, maternal weight gain, and Cesarean rates.

The researchers found no differences between the early treatment group and later treatment group in the primary outcome or any of the other health outcomes.

However, this study had several limitations. This study was stopped early and was very small. It did not have the number of participants that researchers needed to tell whether there was a difference between study groups on their primary outcome. Participants were also not “blinded” to their lab results early in their pregnancy, meaning that all participants knew they had high blood sugar regardless of which treatment group they were assigned to. It’s possible that many people in the study changed their diets and exercise early on (even in the “late treatment” group), which lowered the risk for poor outcomes for everyone.

Specificity and sensitivity are statistical terms that are used to describe how well tests perform in comparison to the gold standard.

Sensitivity refers to how well a test correctly identifies people with the disease, or true positives. This also means fewer false negatives, or people who actually have GDM who screen negatively. Sensitivity is important for GDM screening because we know that it’s important to identify people with GDM so they can manage or treat it and reduce the risk of potential poor health outcomes.

Specificity refers to how well a test correctly identifies people without the disease, or true negatives. This is also important because we don’t want to have a lot of people who don’t actually have GDM to screen positive and need further diagnostic testing or be managed or treated when they might not need it.

Ideally, you want a test to have high sensitivity and specificity. However, there are trade-offs that depend on the severity or impact of the health issue and the cost (financial and emotional) of screening and treatment.

When we’re talking about alternative methods of screening for GDM, most methods are researched in comparison to the OGTT, which is considered the gold standard for GDM screening and diagnosis.

The short answer is that we don’t know for sure whether the sperm used to fertilize the egg can cause GDM. The long answer is a bit complicated (learn more below!), but the suspected link between sperm and GDM has to do with the sperm’s impact on the development of the placenta, and the placenta’s role in the risk for GDM.

There are many genetic and environmental factors that can impact the risk of developing GDM. Hormones from the placenta will cause some level of insulin resistance in everyone who gets pregnant. Hormones also shape the way that the placenta develops, and this can impact how the placenta grows and functions, which can influence the risk for GDM (Calvo et al. 2024). Essentially, the make-up of the placenta and the hormones that it releases can both affect and be affected by GDM.

Researchers have also found that people with GDM are more likely to have placentas with structural changes that impact how well blood flows and how well nutrients and oxygen pass between the birthing person and baby (Carrasco-Wong et al. 2020). Researchers continue to explore the way that hormones and the placenta impact someone’s risk for GDM, and more research is needed (Calvo et al. 2024).

But what does this have to do with sperm? Well, researchers have been studying the ways that epigenetic factors from the male biological parent (or sperm donor, with the case of a sperm donor pregnancy) influence the health of the baby, including how the placenta develops (Bhadsavle & Golding 2022, Khoshkerdar et al. 2021).

Epigenetics has to do with behaviors and environment causing changes that affect the expression of your genes (CDC 2025). Epigenetics are shaped by your health and age and can also be impacted by certain illnesses and diseases or by environmental exposures to things like food insecurity, toxic substances, exposures to trauma, or substance use. Studies have shown that a male partners’ alcohol or cannabis use, diet, body size and other factors can impact epigenetic changes in DNA in the sperm, which can also impact how the placenta develops (Bhadsavle & Golding 2022).

In general, we know that there are connections between the male’s health and epigenetics, and between male health and their sperm quality and the health of the pregnancy and any resulting child(ren). However, we need more research to fully understand the ways that sperm, the placenta, and GDM are connected.

If you are interested in learning more, we recommend checking out the following resources:

• Bhadsavle, S.S., & Golding, M.C. (2022). Paternal epigenetic influences on placental health and their impacts on offspring development and disease. Front Genet 18(13): 1068408.
• Calvo, M.J., Parra, H., Santeliz, R. et al. (2024). The Placental Role in Gestational Diabetes Mellitus: A Molecular Perspective. touchREVIEWS in Endocrinology, 20(1): 10-18.
• Khoshkerdar, A., Eryasar, E., Morgan, H.L. et al. (2021). Reproductive toxicology: Impacts of paternal environment and lifestyle on maternal health during pregnancy. Reproduction, 162(5): F101-F109.

One of the challenges in diagnosing GDM is that many people are not screened for diabetes before pregnancy, so it can be difficult for the provider to tell if GDM is undiagnosed, pre-existing Type 2 diabetes (also referred to as pregestational or overt diabetes) or new onset GDM.

Currently, many professional organizations (including ACOG) recommend that if you have risk factors, you should be screened for pre-existing (pregestational) diabetes early in pregnancy (ideally at their first prenatal visit) (ACOG 2024). People diagnosed with diabetes in the first trimester are classified as having pregestational Type 2 diabetes, instead of GDM. There is disagreement about the best test for Type 2 diabetes in early pregnancy because no approach or diagnostic criteria have been sufficiently validated for pregnancy. Some providers use the one-part diagnostic method, others use the two-part screening and diagnostic method, and others measure hemoglobin A1c (HbA1c) or fasting plasma glucose (FPG) with the same diagnostic criteria that would be applied to nonpregnant people.

If someone has no risk factors, most professional organizations recommend screening for GDM between 24-28 weeks of pregnancy. However, some professional organizations disagree and promote earlier screening for GDM. For example, the IADPSG criteria recommend that everyone, or at least those with risk factors for Type 2 diabetes, be tested at their first prenatal visit with a FPG, HbA1c, or random (non-fasting) plasma glucose test (RPG). They promote diagnosing GDM even in the first trimester in people who do not meet the criteria for pregestational diabetes but have fasting blood sugar levels ≥ 92 mg/dL (IADPSG 2010). Also, they recommend that people who test negative for pregestational diabetes or GDM early in pregnancy still be tested for GDM at 24 to 28 weeks of gestation with an OGTT, since blood sugar problems can increase over the course of the pregnancy.

Other organizations, like ACOG and the U.S. Preventive Services Task Force (USPSTF) have concluded that there is still not enough evidence on the benefits and harms of screening for GDM before 24 weeks of pregnancy (USPSTF 2021; ACOG 2024). There is also a balance between diagnosing GDM early enough so that treatment is effective and the risk of poor outcomes is lowered, but late enough that most people with GDM are identified during screening and diagnosis. That being said, the research on this topic is rapidly growing, and more studies continue to be published. Because of this, some researchers have begun to advocate for early GDM screening and have pushed back against ACOG’s current (2024) recommendations.

For example, Heyborne and Barbour (2025) argue in favor of universal HbA1c screening for pregestational diabetes and targeted early GDM screening. Their reasons for universal pregestational diabetes screening include: 1) an increase in the number of people with risk factors and who meet targeted screening criteria; 2) some of these targeted screening criteria are problematic (e.g., criteria based on race and ethnicity), vague, and difficult to apply; and 3) screening with HbA1c is low cost and easily available.

Basically, Heyborne and Barbour (2025) believe that screening everyone for pregestational diabetes with HbA1c early in pregnancy would help identify people who would benefit from targeted, early GDM screening (focusing only on people whose levels range from 5.9%-6.4%). They cite research suggesting that 40-45% of people who screen positive for prediabetes with HbA1c go on to test positive for GDM (Boe et al. 2019; Hughes et al. 2014). They also point to studies that have shown that pregnant people with prediabetes and HbA1c values within these ranges are at increased risk for health issues like hypertension and big babies (Mane et al. 2017; Sweeting et al. 2017). Although Heyborne and Barbour (2025) acknowledge that more research is needed, they feel that there is enough suggested benefit from recent studies to move towards these screening approaches.

Universal pregestational diabetes screening and early GDM screenings are also advocated for by other researchers and organizations. The ADA now recommends that, in addition to testing people with risk factors, doctors consider testing everyone in pregnancy for pregestational diabetes at their first prenatal visit before 15 weeks (ADA Professional Practice Committee 2025). Durnwald (2025), a medical doctor (MD) and author of the UptoDate article on GDM screening, states that they conduct universal HbA1c screenings with all pregnant patients as part of their routine prenatal labs at the first prenatal visit.

In a recently published article on the “Epidemiology and management of gestational diabetes,” researchers present their argument for why they believe that we should now be screening for early GDM (Sweeting et al. 2024). Their reasoning is based on a set of common principles (Wilson and Jungner criteria) that are often referred to for determining whether population-based screenings should be conducted. Essentially, Sweeting et al. state that we should be screening for early GDM because we know it’s an important issue and we have acceptable and available ways to test for and treat it.  Referring to the Treatment of Booking Gestational Diabetes Mellitus (TOBOGM) trial, they state that early GDM screening and treatment is cost-effective if the following criteria are used (from a 75-gram OGTT): ≥ 5.3 mmol/L, 1-hour post-load glucose ≥ 10.6 mmol/L, or 2-hour post-load glucose ≥ 9.0 mmol/L (or a combination of these).

If you’d like to learn more about the evidence on early screening and treatment for GDM, we’ve summarized it above in the section titled, “New Area of Research: Screening for Early GDM.”

In summary, most professional organizations continue to recommend targeted early screening for pregestational Type 2 diabetes in pregnant people with risk factors. Different organizations then recommend either universal or targeted screening for GDM between 24-28 weeks of pregnancy. Most organizations do not recommend early screening (before 24 weeks) for GDM. However, this is a rapidly growing area of research, and we recommend that you check for current recommendations in your country.

People have asked us if they still need to take the routine glucola screening test if they are healthy and “low risk” for gestational diabetes.

Back in the early 2000s, before universal screening with glucola was normal in the U.S., the American Diabetes Association (ADA) and the American College of Obstetricians and Gynecologists (ACOG) stated that some pregnant people did not need screening for GDM if all of the following criteria were met (Note: ACOG no longer recommends this) (ADA 2003; ACOG 2001):

• Age younger than 25 years
• Not a member of an ethnic group with an increased risk for diabetes (examples include people of Hispanic, African, Native American, South or East Asian, or Pacific Islands ancestry)
• Weight “normal” before pregnancy (BMI ≤25 kg/m2)
• No history of abnormal glucose tolerance
• No history of poor obstetric outcomes
• No close relatives with diabetes

Only about 10% of pregnant people in the U.S. meet all of the above criteria to qualify as low risk for GDM (Danilenko-Dixon et al. 1999). If you fall in that 10%, then you are at very low risk for GDM. However, you can still develop GDM, even if you qualify as low risk. Researchers estimate that about 5% of people who have gestational diabetes would have been labeled as “low-risk” by the ADA-identified criteria (Avalos et al. 2013).

In 2014, the U.S. Preventative Services Task Force (USPSTF) made a recommendation for universal screening with a glucose test at 24 weeks or later (Moyer and USPSTF 2014). Their reason for switching to universal screening with the 50-gram glucola was that most people had one or more risk factors and thus needed to be screened with the glucose test, anyway. Also, trying to identify the small number of people with no risk factors makes the screening process more complex, which would lead to some mistakes where people who do have GDM might go undetected and not receive potentially beneficial treatment.

Selective testing based on risk factors for GDM is still used in some countries today. For example, in the United Kingdom only those with risk factors for GDM are recommended to receive a diagnostic test (NICE 2020).

Right now, we don’t have enough evidence from randomized controlled trials to know if it leads to better outcomes to screen everyone with a 50-gram oral glucose challenge, or just people with risk factors for GDM. A Cochrane review on this topic found only one trial that compared universal screening to selective screening based on risk factors (Tieu et al., 2017). More pregnant people were diagnosed with GDM in the universal screening group; however, the trial didn’t report on birth outcomes for the mother or baby. We also don’t have enough evidence to know if it is better to test everyone with a diagnostic OGTT, or just those with positive screening tests (Farrar et al. 2017a).

What if I want to decline the GDM test?

Having a test for GDM is considered evidence-based care because there are substantial risks if abnormally high blood sugar levels are not identified and treated during pregnancy.

A recently published study looked at health outcomes among pregnant people who chose not to screen for GDM (referred to as “screening nonadherence”) in British Columbia, Canada (Nethery et al. 2025). This study used the British Columbia (BC) birth registry to look at all births with only one baby (singleton births) that happened between 2006 and 2019. The researchers linked the birth registry with other datasets that included insurance information, vital statistics, and census records. To limit the influence of other factors that might impact health outcomes, like starting prenatal care late, they only included people whose care was led by a midwife. Nonadherence to GDM screening is also more common among pregnant people with midwifery-led care and is more likely to be the client’s choice (rather than an issue with access to screening).

The health issues that they looked at in this study included large- and small-for-gestational age babies, 5-minute Apgar scores <7, birth trauma, preterm birth, admission to the NICU, Cesarean birth, 3rd and 4th degree perineal tears, and stillbirth (which they defined as birth of a fetus at ≥ 20 weeks’ of pregnancy or with a birth weight ≥ 500 grams and showing no signs of life at birth). In their analysis, the researchers controlled for other factors that can impact these outcomes, like maternal age, pre-pregnancy BMI, pre-pregnancy risk factors for poor outcomes, and maternal smoking.

This study looked at a total of 83,522 pregnancies. The researchers compared outcomes between those who completed standard GDM screening and had normal results (57,750  people in the “normal blood sugar” group) to those in three “non-adherent” groups: 1) those who did not do any testing (17,866 people); 2) those who did early non-standard screening like with an HbA1c or RPG test (4,584 people) and; 3) those who did non-standard screening with an HbA1c or RPG test between 20 and 30 weeks of pregnancy (3,322 people).

Compared to the standard GDM screening “normal blood sugar” group, midwifery clients who did not do any testing had a lower risk of large-for-gestational age babies and Cesarean, but a higher risk of stillbirth and small-for-gestational age babies. They did not find differences in any of the other outcomes.

The researchers also wanted to see if there were differences in outcomes between people with and without pre-pregnancy risk factors for GDM in the non-testing group. They found an even higher risk of stillbirth in those with risk factors (2.5 times higher). However, the researchers note that there is the possibility that people who declined GDM screening might have also declined other interventions (e.g., screenings for fetal anomalies or treatments) that could have also increased their risk for stillbirth. The researchers note that “our findings strongly support screening for those with pre-pregnancy GDM risk factors.”

The researchers in this study also compared people in the other two nonadherent screening groups (early non-standard screening and non-standard screening between 20-30 weeks) to those in the standard GDM screening “normal blood sugar” group. They did not find many differences in outcomes between groups, but this may have been because they did not have as many people to compare. However, they did find that people in each of the three nonadherent groups (no testing, non-standard early screening, non-standard screening between 20-30 weeks) had a consistently lower risk of Cesarean.

It is a human right to decline medical treatment unless the individual is formally found to be incapable of making medical decisions. In the U.S., ACOG has affirmed that pregnant people with GDM have the right to individualized care and the right to refuse care (ACOG 2018):

This information [about gestational diabetes] should not be considered as inclusive of all proper treatments or methods of care or as a statement of the standard of care…Variations in practice may be warranted.

ACOG’s Committee on Ethics states that:

Pregnancy does not lessen or limit the requirement to obtain informed consent or to honor a pregnant woman’s refusal of recommended treatment.

(You can read the full text of ACOG’s statement on “Refusal of Medically Recommended Treatment During Pregnancy” here: ACOG, 2016, Reaffirmed 2019).

There is a lot of discussion about the best way to diagnose gestational diabetes. But perhaps a more important question is, does treatment actually lead to a benefit for the mother or baby? A systematic review and meta-analysis by Farrar et al. (2017b) include 42 trials, two of which are large and of high-quality (Crowther et al. 2005; Landon et al. 2009). The findings suggest that treatment does improve the health of the mother and baby.

Many of the included studies compared different medications (insulin, metformin, or glibenclamide/ glyburide). However, we are going to focus on the 12 trials that compared ‘bundles of care’ (starting with lifestyle changes then using medication as necessary to lower blood sugar levels) versus routine care. The reason we are focusing on the trials that looked at bundles of care is because that is the recommended approach for treating mothers with GDM—exercise and nutrition counseling as the first line of action, followed by medication if values are routinely greater than or equal to target values (ACOG 2018). It’s estimated that about 40% of people diagnosed with GDM (using IADPSG criteria) require medication, usually insulin, to manage their blood sugar levels (Bogdanet et al. 2017).

The meta-analysis found that bundles of care cut the risk of large birth weight by 50% and shoulder dystocia by 60%. They did not find a significant difference in the risk of pre-eclampsia, Cesarean, newborn intensive care, newborn low blood sugar, preterm birth, low Apgar scores, use of forceps/ vacuum, or labor induction. In two of the trials, participants reported higher quality of life after treatment for GDM.

Different professional organizations have different recommendations on inducing labor in people with GDM, and sometimes these recommendations depend on how well blood sugars are managed or controlled in the pregnant person. For example, in people who have well-controlled blood sugar with diet and exercise, the American College of Obstetricians and Gynecologists (ACOG) recommends expectant management (waiting for labor to begin spontaneously) through 40 weeks and 6 days. For people with well-controlled blood sugar with medication, ACOG recommends birth between 39 weeks and 0 days to 39 weeks and 6 days (ACOG 2018, Reaffirmed 2024).

There haven’t been enough randomized controlled trials and evidence to show that inducing labor at 38 or 39 weeks in everyone with GDM is beneficial. Evidence from some observational studies suggests that people with GDM who give birth at 39 or 40 weeks had a lower relative risk of perinatal death compared to those whose pregnancies go beyond 40 weeks, but the absolute risk of perinatal death was still low overall.

We have much more information about induction for people with GDM in our Signature Article on this topic, “Evidence on: Induction for Gestational Diabetes.”

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The book Real Food for Pregnancy [https://realfoodforpregnancy.com/] by Lily Nichols, RDN, CDE, is a great source of information on eating well throughout the entire pregnancy. She also has a book called Real Food for Gestational Diabetes (https://realfoodforgd.com/) for people who have been diagnosed with GDM and want to try and manage their blood sugar levels with diet. Ms. Nichols is a specialist in gestational diabetes and prenatal nutrition. Both books are evidence-based resources with citations to the research articles she used to formulate her recommendations.