Gestational diabetes (GD) is traditionally diagnosed between 24–28 weeks of pregnancy, but emerging research suggests that blood sugar imbalances may be happening early on during pregnancy.

I’ve written at length about gestational diabetes screening (see chapter 9 of my book, Real Food for Pregnancy), but I still receive a fair amount of questions on screening options. Some organizations advocate for early screening for gestational diabetes, particularly in individuals with existing risk factors that could put them at higher risk. 

In the past few years, as access to continuous glucose monitors (CGM) has improved, many are asking me if this is a potential option for screening for gestational diabetes, even in early pregnancy.

The general line of reasoning is that since we know gestational diabetes is often seen in individuals with underlying insulin resistance, could we learn earlier than 24–28 weeks whether there are any blood sugar imbalances and, if so, could we intervene earlier to help improve the outcomes of their pregnancy?

I’m covering these questions and more in this article.

Early Gestational Diabetes Screening: The Research on Monitoring Blood Sugar Earlier in Pregnancy

So the major question at hand is: Should we be screening for gestational diabetes earlier? A 2024 study using continuous glucose monitoring (CGM) has helped to answer this question. 

This study (detailed below) found that blood sugar imbalances were already present in early pregnancy among women who later developed gestational diabetes. These findings could revolutionize how we screen for and manage gestational diabetes.

Early Pregnancy Blood Sugar Imbalances: What the Research Says

A 2024 study involving 768 pregnant women tracked glucose levels continuously starting before 17 weeks of pregnancy. Participants wore CGMs that provided 24/7 blood sugar data throughout pregnancy. Later, they all underwent standard gestational diabetes screening with a glucose tolerance test at 24–28 weeks.

The results showed significant differences in blood sugar patterns, as early as 13-14 weeks of pregnancy, between those who were later diagnosed with GD and those who were not:

• Mean glucose levels were 109 mg/dL (6.0 mmol/L) – significantly higher than in the non-GD group (100 mg/dL or 5.6 mmol/L).
• Glycemic variability was significantly greater in the GD group versus the non-GD group (meaning greater swings in blood sugar levels).
• Nighttime glucose levels averaged about 9 mg/dL higher in the GD group versus the non-GD group (again, statistically significant).
• The amount of time that glucose levels stayed within the target range was significantly lower – 87% in the GD group vs. 94% in the non-GD group. 

These findings indicate that blood sugar dysregulation in pregnancy begins much earlier than previously assumed and that standard screening may be catching GD too late. This is a missed opportunity for earlier dietary/lifestyle counseling to help maintain blood sugar within the healthy range for a larger proportion of the pregnancy.

Why Continuous Glucose Monitoring (CGM) Could Change Gestational Diabetes Screening

The study suggests that CGM could be a game-changer for early GD detection and management. By identifying high blood sugar patterns before the traditional screening window, CGM may allow for earlier dietary and lifestyle interventions, potentially preventing complications associated with gestational diabetes.

CGM technology has gained popularity in recent years, and while it was once restricted to prescription use (I allude to this in my previous “CGM Experiment” articles, the first of which I published in 2018), some simplified CGM systems have now been approved for over-the-counter access in the U.S. This increased accessibility may allow more pregnant women to track their blood sugar levels in real-time and take proactive steps to maintain optimal glucose control.

There’s also a number of companies that offer CGM without having to consult your own healthcare provider, like Levels, though these are not always available if you are pregnant.

One of the perks of CGMs over an ordinary fingerstick glucometer is that you can watch blood sugar fluctuations throughout the day and night, offering far more insight than intermittent fingerstick readings. You can see how quickly or slowly different foods change your blood sugar levels and make more informed decisions about your diet and lifestyle.

Keep in mind that interpreting CGM data requires some expertise. Pregnancy-specific glucose targets differ from non-pregnant values, and blood sugar responses can be influenced by multiple factors, including diet, sleep, stress, hormonal fluctuations, and more.

The Challenges and Benefits of CGM for Gestational Diabetes Management

As a dietitian who has worked with thousands of clients, I’ve found that CGMs provide invaluable insights but also require guidance to interpret effectively. In recent years, many of the women in my Real Food for Gestational Diabetes Course have used CGMs, and with proper support, they’ve been able to fine-tune their dietary and lifestyle habits for better blood sugar control and healthier pregnancy outcomes.

One major challenge that affects approximately 60% of women with gestational diabetes is high fasting blood sugar. This is a really tricky one to manage clinically because there are several possible blood sugar patterns occurring overnight. With the help of a CGM, we can better see what’s happening and target the intervention appropriately. It is the unfortunate reality that most women are told that there is nothing they can do with their diet or lifestyle to lower fasting blood sugar — and that’s not necessarily true! I know because I’ve worked firsthand with countless women facing this challenge. I even devote an entire training in my Real Food for Gestational Diabetes Course to the topic of troubleshooting high fasting blood sugar! That is the only place (outside of my formal practitioner mentorship program) that I teach this information, by the way.

While CGM use in pregnancy is still gaining traction, its potential to revolutionize early gestational diabetes detection cannot be ignored. If higher glucose levels are already detectable at 13–14 weeks, should we be revising our screening guidelines to catch GD sooner? Possibly!

What About Using HbA1c for Gestational Diabetes Screening?

Using hemoglobin A1c (HbA1c of A1c) to screen for gestational diabetes in early pregnancy is gaining interest, especially for identifying women at higher risk of developing GDM later on. A1c reflects average blood glucose levels over the previous two to three months, so testing in the first trimester can highlight preexisting insulin resistance or even undiagnosed type 2 diabetes.

This is why the California Diabetes and Pregnancy Program: Sweet Success has long recommended universal first trimester screening with A1c. Any individuals with an A1c of 5.7% or higher are classified as having gestational diabetes (it’s technically prediabetes, but nonetheless, their dietary recommendations and blood sugar monitoring follows the same trajectory as someone diagnosed with gestational diabetes).

An elevated A1c (often defined as ≥5.7%) has been linked to a significantly increased risk of developing GDM (i.e. “failing” a glucose tolerance test) and other pregnancy complications. In fact, studies have found that a high first trimester A1c accurately predicts gestational diabetes (confirmed by OGTT) 94 to 99.8% of the time, depending on the study population. Since this test is non-fasting, inexpensive, and widely available, it offers a practical way to identify at-risk women early in pregnancy.

One of the main advantages of using A1c early is that it allows for earlier lifestyle and dietary interventions — and this minimizes the adverse risks of gestational diabetes on the developing baby. Early action may reduce the risk of common GDM-related complications like excessive fetal growth (macrosomia), preeclampsia, or the need for cesarean delivery.

For these reasons, some providers now include A1c testing as part of routine first-trimester labs, especially in women with risk factors such as elevated BMI, family history of diabetes, or PCOS. You’ll recall from Real Food for Pregnancy that I’m a strong advocate for measuring first trimester A1c. We used it routinely in the perinatology practice I used to work for and I advocated for this lab test in both of my pregnancies as well.

However, there are limitations. A1c is less sensitive than a glucose tolerance test or continuous glucose monitoring (CGM) in detecting subtle blood sugar issues. For example, someone with a normal A1c can have dramatic blood sugar swings or excessively high insulin levels. Furthermore, physiological changes in later pregnancy — such as increased red blood cell turnover and hemodilution — can lower A1c values artificially if it is drawn in the second and third trimesters. This is why A1c CANNOT be used as an alternative diagnostic test for gestational diabetes in the second or third trimesters.

While useful for flagging risk early on in pregnancy, getting a normal A1c in the first trimester also does not replace formal screening later in pregnancy (typically at 24–28 weeks). 

For more information on the pros/cons of different screening methods for gestational diabetes, be sure to read chapter 9 of Real Food for Pregnancy! I cover them all, including the jelly bean test, test meals, juice, different versions of the oral glucose tolerance test, home monitoring, and more!

What This Means for Healthcare Providers

The implications of this research are significant. Screening earlier for gestational diabetes could help women take action before high blood sugar causes complications, such as:

• Excessive fetal growth (macrosomia)
• Preeclampsia
• Preterm birth
• C-section delivery

A 2022 study published in JAMA Network Open examined how blood sugar control throughout pregnancy affects outcomes for women with gestational diabetes (GD). The researchers tracked blood glucose levels in women with GD and found that those who achieved and maintained good glycemic control earlier in pregnancy had significantly lower risks of complications, including a lower risk of having a high birth weight infant, giving birth preterm, or needing a C-section delivery. 

If you’re a clinician, it’s vital to stay up-to-date on evolving GD management strategies and to help clients achieve blood sugar balance quickly after diagnosis. CGM could be a powerful tool, but guidance is key here. As a clinician, it can also take a while to get used to interpreting CGM data. I highly recommend doing your own CGM experiments on yourself, and additionally, getting support from a mentor if your speciality is not in diabetes.

Where to Learn More About Gestational Diabetes Screening and Management

If you’re looking for more resources on gestational diabetes prevention and management, here are some key resources:

• For info on gestational diabetes screening, such as the glucose tolerance test, and whether there are viable alternatives, see chapter 9 of Real Food for Pregnancy. Remember, that even if your blood sugar levels look great in early pregnancy, you want to have a plan for gestational diabetes testing at 24-28 weeks. Even if some cases of gestational diabetes show early pregnancy glucose imbalances, not all cases do. It absolutely can develop later in the pregnancy.
• For info on strategies to help prevent gestational diabetes, if you’re already pregnant, see chapter 7 of Real Food for Pregnancy. It covers a number of dietary and lifestyle strategies for reducing the risk of developing gestational diabetes. If you’re not currently pregnant and have risk factors, like PCOS, apply all of the tips in the PCOS chapter as well as all of the chapters on nutrition in Real Food for Fertility.
• If you get diagnosed with gestational diabetes, check out my book, Real Food for Gestational Diabetes. It’s the number 1 bestselling book on GD for good reason: the advice in it works. It has even influenced gestational diabetes policies internationally.
• If you need additional support managing your gestational diabetes beyond what’s covered in my books — such as advanced strategies for managing high fasting blood sugar, meal plans, access to my input during office hours, a community of support, and SO much more — check out my online gestational diabetes course. This is the only place that I can answer your specific questions on gestational diabetes.
• If you are a clinician seeking mentorship in gestational diabetes management, there is an entire module in the Institute for Prenatal Nutrition mentorship program on gestational diabetes. Since this is the most common pregnancy complication, by far, it’s imperative that anyone claiming to have expertise in prenatal nutrition has the proper training to address GD management with their clients. I don’t know of any other program that covers the diagnosis in enough detail. If you want to be notified when we open applications for the next class, make sure you get on the waitlist.

Until next time,

Lily

PS – If you received early screening for gestational diabetes in your pregnancy, tell us about it in the comments below. Did your provider have you check your blood sugar at home with a CGM or glucometer? Did they test your A1c? What did you learn from that process?

 

References

• Durnwald, Celeste et al. “Continuous Glucose Monitoring Profiles in Pregnancies With and Without Gestational Diabetes Mellitus.” Diabetes care vol. 47,8 (2024): 1333-1341. 
• Osmulski, Meredith E et al. “Subtypes of Gestational Diabetes Mellitus Are Differentially Associated With Newborn and Childhood Metabolic Outcomes.” Diabetes care vol. 48,3 (2025): 390-399.
• Chehab, Rana F., et al. “Glycemic control trajectories and risk of perinatal complications among individuals with gestational diabetes.” JAMA Network Open 5.9 (2022): e2233955-e2233955.
• Osmundson, Sarah S et al. “First Trimester Hemoglobin A1c Prediction of Gestational Diabetes.” American journal of perinatology vol. 33,10 (2016): 977-82.
• Sun, Jianbin, et al. “Predictive value of first‐trimester glycosylated hemoglobin levels in gestational diabetes mellitus: a Chinese population cohort study.” Journal of Diabetes Research 2021.1 (2021): 5537110.
• Majewska, Agata, et al. “Efficacy of continuous glucose monitoring on glycaemic control in pregnant women with gestational diabetes mellitus—a systematic review.” Journal of Clinical Medicine 11.10 (2022): 2932.