Managing Your Glucose and Using a Continuous Glucose Monitor During Pregnancy
By Dr. Sarit Polsky
Keeping glucose levels in a tight range is more important than ever during pregnancy. Dr. Sarit Polsky discusses glucose management and target glucose levels, as well as the benefits of using continuous glucose monitors (CGM), for pregnant women with diabetes.
Pregnancy can be both exciting and stressful. Pregnancies associated with diabetes are complex and often involve concerns of health risks to mothers and to their babies. We recommend that women with diabetes start planning for pregnancy with support from their diabetes healthcare professionals before stopping contraception (most women take a few months to reach their target glucose levels). Women with diabetes should start working with their diabetes and obstetric providers early on in their pregnancy, and continue prenatal care with an experienced and supportive team. One of the most important things you can do to support a healthy pregnancy and a healthy child is to carefully manage your glucose levels.
Glucose management during pregnancy
Glucose management is a critical aspect of improving the chances of a healthy pregnancy and of reducing the risks to moms and their babies. Ideally, we aim to keep glucose levels at normal or near-normal levels. Most expert guidelines recommend:
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The mother’s A1C should be under 6.5% before conception and during pregnancy, with some recommending an A1C under 6.0% as the pregnancy progresses.
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Glucose levels before meals and overnight should be below 95 mg/dL, and below 140 mg/dL after meals.
While it can feel overwhelming to have to tightly regulate glucose levels before and during pregnancy, the good news is that there are tools that can help.
What are continuous glucose monitors and why are they helpful?
Continuous glucose monitoring (CGM) can be very beneficial during a pregnancy. CGMs have a sensor inserted in your skin to check your glucose levels every 1 to 5 minutes (the sensor measures glucose between your cells, called your interstitial glucose, not to be confused with your blood glucose). The sensor then transmits your glucose levels to a receiver device, an insulin pump, a smart phone, or a smart watch. If the system transmits data continuously and gives you alerts when your glucose is above or below certain levels, it’s called a real-time CGM. If the system does not provide alerts and you can only see your glucose when you scan the sensor, then it’s called an intermittently-scanned CGM. Depending on the CGM, the sensor can stay on your skin for anywhere from 6 to 14 days (and implantable sensors can last up to 90 days under the skin).
CGM systems give you a tremendous amount of information. If your CGM checks glucose every five minutes, you get about 288 glucose data points each day. This allows you to see what your glucose levels do during times when you may be less likely to check a fingerstick glucose level, like during sleep or after meals. You can also see trends over time. For example, spikes in glucose levels for particular meals. CGM can also help you prevent serious health complications resulting from very low or very high glucose. If you consistently wear the CGM and use the information it provides to inform your diabetes management, you can improve your glucose levels. There are some risks and challenges to using a CGM, so consult with your healthcare professional before starting the technology.
CGM use during pregnancy
What about the use of CGM in pregnancy? Studies have shown that it’s much easier to see how variable glucose levels are (high and low values throughout the day and between days) when using a CGM compared to fingerstick glucose testing. Not only that, but CGM use – from multiple CGM systems including Medtronic, Abbott, and Dexcom – has been evaluated in pregnant women with type 1 diabetes, type 2 diabetes, and gestational diabetes and has been found to be both safe and accurate during pregnancy. The use of CGM in pregnancy has also been shown to improve the health of the babies through better management of maternal glucose levels. The babies of mothers who use CGM are less likely to have abnormally high birthweight and severely low glucose levels after birth, have fewer admissions to newborn intensive care units, and shorter infant hospital admissions.
Many guidelines currently recommend the use of CGM in pregnancies associated with type 1 diabetes. Some studies suggest that CGM use may also be beneficial for pregnant women with type 2 diabetes and gestational diabetes. Unfortunately, CGM use is not FDA-approved for use during pregnancy in the US, though many women use the technology “off-label.” CGM is cleared for pregnant women in Europe, has been temporarily approved for pregnancy in Canada during the COVID-19 pandemic, and is funded by the government for use by all pregnant women with type 1 diabetes in the UK.
In 2019 an expert panel convened of diabetes care professionals, researchers, and people living with diabetes convened. It recommended the following Time in Range goals for pregnant women with type 1 diabetes:
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Less than 4% of time spent with CGM values of 63 mg/dL or less (Time Below Range, TBR);
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More than 70% of time spent with CGM values of 63-140 mg/dL (Time in Range, TIR);
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Less than 25% of time spent with CGM values above 140 mg/dL (Time Above Range, TAR).
Because of limited data, the panel did not recommend a specific goal for the percentage of time spent in the pregnancy target range for gestational diabetes or pregnant women with type 2 diabetes.
Why do we aim for a Time in Range of above 70%?
One of the crucial studies that helped support this recommendation was the CONCEPTT study (Continuous glucose monitoring in pregnant women with type 1 diabetes). In CONCEPTT, 215 pregnant women and 110 women planning pregnancy who had type 1 diabetes were given a random assignment to do self-monitoring of blood glucose (SMBG) through fingerstick glucose testing, or to use a CGM with SMBG throughout pregnancy. CGM measurements were collected for both groups at multiple time points, but women in the SMBG group could not see their CGM values.
While there was only a small difference in A1C between pregnant women in the CGM and SMBG groups (6.35% and 6.53%, respectively), the study found a big difference in glucose management.
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The CGM group had a significantly higher Time in Range (68% with CGM versus 61% with SMBG, a difference of about 1.5 hours per day).
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The CGM group had lower Time Above Range (27% with CGM versus 32% with SMBG, a difference of about 1.2 hours per day).
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The CGM group had significantly improved health outcomes for the babies, including: a lower rate of abnormally large babies, a lower rate of babies needing intravenous glucose for low sugars, fewer infants requiring high-level care for more than 24 hours (newborn intensive care unit admissions), and a shorter hospital stay for babies by about one day.
- These health benefits seemed to occur when the mother wore the CGM most of the time (about 70% of the time or more).
With this being said, A1C is still important, and higher A1C levels have been consistently shown to increase risks for mothers and babies across studies. However, CONCEPTT indicates that A1C may not be the only important glucose measurement – Time in Range can be a meaningful additional indicator of diabetes management. The ability to manage glucose levels both overall and within each day through CGM data helps improve health during pregnancy, as demonstrated by the CONCEPTT study.
Another study, in Sweden, looked at 186 previous pregnancies of women with type 1 diabetes using CGM to see if the CGM data related to health outcomes. Researchers found that in the second and third trimesters, lower average glucose levels, higher TIR, lower TBR and TAR, and less second trimester glucose variability were all associated with lower rates of abnormally large babies.
Both studies helped determine how small increments in TIR affect health during pregnancy. Even having a higher TAR 5% of the time (for example, 30% TAR versus 25%) and a lower TIR 5% of the time (for example, 65% TIR versus 70%)in the second and third trimesters increases the risk of abnormally large babies, severe hypoglycemia in the baby, and a high-level hospital admission for babies.
What can you do?
Work with your healthcare professional to determine if CGM therapy is right for you during your pregnancy. If so, try to wear the CGM as much as possible for your entire pregnancy. Remember that your A1C, while very important, cannot tell the whole story of your glucose levels each day.
Work with your healthcare team to alter insulin dosing and react to changes in glucose levels using data from your CGM. Changes in diabetes management based on CGM data have been proven to lead to better health outcomes, particularly for your baby. Even small improvements – like increasing the time spent in the pregnancy target glucose range (63-140 mg/dL) by 5% – can make a big difference for the health of you and your child. CGM won’t fully replace fingerstick glucose testing during pregnancy but will be used alongside it.
Finally, I tell pregnant women with type 1 diabetes that it is possible for them to have happy and healthy pregnancies, but they will have to work harder than women without diabetes, both before and during pregnancy. CGM is a tool that can help them and you successfully manage glucose levels throughout pregnancy.
This article is part of a series on time in range.
The diaTribe Foundation, in concert with the Time in Range Coalition, is committed to helping people with diabetes and their caregivers understand time in range to maximize patients' health. Learn more about the Time in Range Coalition here.
About Sarit
Sarit Polsky, MD, MPH is an Assistant Professor of Medicine and Pediatrics at the University of Colorado Anschutz Medical Campus. Dr. Polsky joined the staff at the Barbara Davis Center (BDC) for Diabetes in 2014 and is the director of the Pregnancy and Women’s Health Clinic.
Dr. Polsky currently has research grants from foundation, government, and industry agencies to examine the use of advanced diabetes technologies and therapeutics to improve health outcomes in people with type 1 diabetes, including pregnant women. Her technology research has utilized numerous insulin pumps, continuous glucose monitoring systems, and automated insulin delivery systems in adults with type 1 diabetes. She is the Principal Investigator for the first study in the United States approved by the FDA to examine artificial pancreas technology in pregnancies associated with type 1 diabetes.
Dr. Polsky continues to care for people with diabetes at the BDC. She has given numerous talks at academic institutions, professional society meetings, and community educational events. She is passionate about educating her patients and the community about women’s health in diabetes.
