Assessing Glycemia during Pregnancy: Where are We Now?

photograph of the author
Author
Sarit Polsky
photograph of the reviewer
Medically reviewed by
Sarit Polsky, MD, MPH
Published On
November 3, 2025
Updated On
November 3, 2025

Thanks to advances in insulins, research, and technology, supporting people with diabetes through a safe pregnancy and birth is more possible than ever. While pregnancies associated with diabetes face a higher risk for complications like fetal loss, birth defects, large babies, preeclampsia, early delivery, and operative deliveries1-5 we know that tight glycemic management can reduce these risks.

A1C is commonly used to monitor and manage diabetes-related risks in pregnancy. Years of research have established correlations between A1C and pregnancy outcomes, informing recommendations that providers work with pregnant people to reach levels less than 6.5% in the first few weeks of pregnancy to reduce rates of birth defects.5

While A1C is a valuable tool, it is important to know there are limitations of this measurement during pregnancy. A1C measures the glycation, or bonding, of glucose to hemoglobin in red blood cells, which have a limited life span (about 3 months). In pregnancy, red blood cells are produced at a faster rate. Higher turnover of red blood cells and the significantly increased blood volume in pregnancy dilute the proportion of glycated hemoglobin, which lowers A1C. This can also be seen in women without diabetes, who have lower A1C levels in pregnancy compared to outside of pregnancy.6

When helping those in your care reduce risk of adverse pregnancy outcomes, keep in mind that A1C levels may appear lower regardless of glycemia. Additionally, as an average, A1C cannot provide the detailed information within and between days that is needed to manage diabetes during this critical period. It cannot capture important patterns such as high glucose levels after meals.1 This is why practice guidelines recommend checking glucose levels before and after meals, in addition to measuring A1C levels, throughout pregnancy.1

Continuous glucose monitoring (CGM) is playing a growing role in pregnancy, as evidence supporting its benefits to user experience and pregnancy outcomes continues to grow. 

In type 1 diabetes pregnancies, the use of CGM throughout gestation has been associated with lower A1C levels in a large randomized controlled trial (RCT, the CONCEPTT trial)7 and a real-world study.8 While the CONCEPTT trial showed minor improvements in A1C among those using CGM compared to self-monitoring of blood glucose (SBMG) (mean difference 0.19% at 34 weeks), both groups had A1C levels close to the pregnancy goal of <6% in the 3rd trimester (6.35% in the CGM group vs 6.53% in the fingerstick testing group). Despite the minor difference in A1C, the infants born to those using CGM had a significantly lower risk of being large-for-gestational age, having severe neonatal hypoglycemia requiring IV dextrose, and needing admission to the neonatal intensive care unit7 The reason for these neonatal health gains is that using CGM increased the maternal time spent in the optimal glucose pregnancy time in range (TIRp, 63-140 mg/dL) and decreased the time spent above range (>140 mg/dL).9 This RCT demonstrated that while the A1C level is important, it doesn’t relay the whole story.

The results of the CONCEPTT trial also highlight the limitations of SMBG testing. Even if a pregnant woman is checking her blood glucose multiple times a day (e.g., before and after meals and at bedtime), she won’t have as many measurements as with a CGM device (e.g., 288 measurements/day). Additionally, if she checks her glucose once after a meal and once during the night, she may not be checking at the highest peak of her glucose level after that meal or during that night, respectively. Importantly, some women also report more satisfaction with CGM use.

CGM provides detailed, actionable data in real-time and the ability to see glucose trends at times when levels vary considerably (e.g, after meals) or when pregnant people are unable to check (e.g. while sleeping). Like A1C, CGM metrics like TIRp can also predict pregnancy outcomes.2-4 In type 1 diabetes, every additional 5% spent in TIRp is associated with reduced risk of having a large-for-gestational-age infant, neonatal hypoglycemia, and neonatal intensive care unit admissions.10 There remain some unanswered questions about CGM use in type 2 diabetes pregnancies and gestational diabetes, like whether neonatal health benefits are the same as those observed in type 1 diabetes studies and cost-effectiveness, but the technology holds promise for these groups as well.

Effectively managing glucose levels throughout pregnancy is essential to significantly reducing risks to mothers and babies. While A1C remains an important measurement for assessing overall glycemic status in gestation, it is important to note that obtaining glucose measurements throughout the day and night is still needed. CGM has emerged as a key complementary tool to contextualize A1C levels and effectively manage glucose within a day and from day-to-day, improve treatment satisfaction, and predict adverse health outcomes in pregnant women, particularly those with type 1 diabetes. 

 

Get started with CGM and time in range in your practice today!

 

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