What your A1c can (and can’t) tell you during pregnancy

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Author
Sarit Polsky
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Medically reviewed by
Sarit Polsky, MD, MPH
Published On
November 3, 2025
Updated On
November 4, 2025

Having a safe pregnancy and birth while living with diabetes is more possible than ever. Thanks to advancements in insulin therapy, diabetes technologies, and clinical care, you can reduce your risk for pregnancy complications that are more common with diabetes.1

If you’re living with diabetes and thinking about planning a pregnancy, you may have heard it’s best to work towards an A1C below 6.5% before conceiving or as soon as possible after, then aim for an A1C below 6% further along into the pregnancy. This advice comes from research which shows that as A1C increases in pregnant women with type 1 diabetes, type 2 diabetes, and gestational diabetes, risks for outcomes like fetal loss, birth defects, large babies, preeclampsia, early delivery, and operative deliveries also increase.2-4 For example, when A1C is reduced below 6.5% within the first few weeks of pregnancy, the risks of birth defects are significantly lower5—but did you know that pregnancy can impact your A1C, regardless of your glucose levels? 

A1C measures how much glucose is attached to your red blood cells, which have a life span of about 3 months. In pregnancy, red blood cells are produced at a faster rate. This higher turnover of red blood cells, plus significantly increased blood volume in pregnancy, dilutes the amount of glucose attached to the red blood cells, lowering the A1C.6

What does this mean for monitoring glucose levels during pregnancy? 

First, your A1C may appear lower, and not reflect your average glucose in the same way it did before pregnancy. Second, an A1C only provides a snapshot of glucose levels—an average at one point in time. During pregnancy, when management is particularly important for the development and health of you and your baby, more frequent, detailed information on glucose levels is not only helpful, but necessary to capture the highs, lows, and significant day-to-day changes that occur. That’s why medical guidelines recommend checking glucose levels frequently (especially before and after meals).1

CGM and its metrics, like time in range, can help track these details and identify patterns, providing actionable data in real-time and the ability to see glucose trends at times when levels vary considerably (like after meals) or when you’re not able to check (while sleeping, for example). Research has even shown that time in range data, not just A1C levels, can predict pregnancy outcomes such as large babies or neonatal hypoglycemia!2-4

In type 1 diabetes, every additional 5% spent in the target pregnancy range (63-140 mg/dL) is associated with reduced risks of having a large-for-gestational-age infant, neonatal hypoglycemia (low blood sugar), and neonatal intensive care unit admissions.7 A study comparing use of CGM and fingerstick testing in T1D pregnancies found that A1C was slightly lower among those who used CGM, but the time spent in the pregnancy range was much higher and time spent above the pregnancy range (>140 mg/dL) was much lower, which lead to risk of some adverse outcomes being substantially lower.8-9 This shows that while A1C is important, it doesn’t tell the whole story. More research is needed about CGM use in pregnancy with type 2 and gestational diabetes, but the technology holds promise in these cases, too. 

To sum it up: A1C can help you and your healthcare team monitor and reduce risks in pregnancy, and CGM and its metrics contribute complementary information to further understand your glucose levels. Using the information obtained through CGM can change the game by providing metrics that can help monitor and manage risks—at more frequent, timely intervals than an A1C. 

Learn more about how time in range can help you!

 

  1. Section 15: Management of Diabetes in Pregnancy. Clin Diabetes. Spring 2025;43(2):223-224.
  2. Meek CL, Feig DS, Scott EM, Corcoy R, Murphy HR, Group CC. Lack of Validity of the Glucose Management Indicator in Type 1 Diabetes in Pregnancy. Diabetes Care. Apr 2 2025.
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  4. Li Z, Beck R, Durnwald C, et al. Continuous Glucose Monitoring Prediction of Gestational Diabetes Mellitus and Perinatal Complications. Diabetes Technol Ther. Nov 2024;26(11):787-796.
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  9. Garg SK, Polsky S. Continuous glucose monitoring in pregnant women with type 1 diabetes. Lancet. Nov 25 2017;390(10110):2329-2331.