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New Look at CGM in Expecting Mothers

Jul 21, 2020
Editor: David L. Joffe, BSPharm, CDE, FACA

Author: Maya Palmer, PharmD. Candidate, Florida A&M University College of Pharmacy

Evidence suggests that pregnant women with type 1 diabetes can achieve optimal glucose control based on temporal glucose profiles.  

A mother’s maternal glucose significantly determines fetal growth. A mother’s glycemic levels can also forecast if an infant will be large for gestational age as well as overall neonatal outcomes. Studies conducted have proven a direct tie from in utero exposure to higher levels of maternal glucose to the infant experiencing insulin resistance and high blood glucose levels during childhood. Continuous glucose monitoring (CGM) is the most helpful method for expecting mothers to assess their varying blood glucose levels. However, one key factor remains missing about this method—it does not offer a fundamental analysis of levels in a time series. Expecting mothers with diabetes are unable to receive temporal glycemic information. This study applies analysis to learn if temporal glucose profiles differ between particular factors in pregnant women with type 1 diabetes.  

For this study, researchers looked at comparisons between women who were randomized to real-time continuous glucose monitoring (RT-CGM) or self-monitored blood glucose (SMBG), women who used insulin pumps or multiple daily insulin injections (MDIs), and women whose infants were born large for gestational age (LGA) or not. CGM data were assessed from the Continuous Glucose Monitoring in Women with Type 1 Diabetes in Pregnancy Trial (CONCEPTT) by functional data analysis (FDA) at baseline, 24, and 36 weeks’ gestation. The CONCEPTT trial had previously established the relationship between RT-CGM and improved neonatal outcomes compared to women who used SMBG. FDA was used to demonstrate sensitivity at detecting shorter periods of high blood glucose levels, which allowed mothers to know precisely which time frames of hyperglycemia occurred within a 24-hour day. The mean of four or more days of temporal CGM data was collected from participants at each glucose time point taken throughout the 24-hour day. A multivariable regression analysis evaluated temporal differences in glucose profiles within 24 hours between the three comparison groups.  

At 34 weeks, the group of women who used RT-CGM had the most time spent in pregnancy glucose target range compared to the group who used SMBG. These women also had lower blood glucose levels (by 7-14 mg/dL) for seven hours during the day compared to SMBG. For the next group of women who used insulin pumps, significantly lower blood glucose levels were found (by 7-16 mg/dL) for nearly six hours out of the day. Strikingly though, for 12 hours out of the day, this group had higher levels (by 7-16 mg/dL) at 24 weeks gestation. Furthermore, the group of women who had LGA infants was detected to have higher mean glucose levels (by 7-13 mg/dL) at both 24 and 34 weeks for close to five hours a day, versus the group who did not. Day and night levels were higher for this group for 16 hours a day at 24 weeks (by 7-16 mg/dL); however, it was only high at night for 14 hours a day at 34 weeks.  

Women who used RT-CGM were confirmed to have lower blood glucose levels during the daytime than women solely using SMBG. This evidence can better assist expecting mothers to monitor their carbohydrate intake during the day to try to alleviate unexpected fluctuations. Women who used insulin pumps showed better blood glucose control in the first trimester; yet, as the pregnancy progressed to 24 weeks, the analysis revealed worse daytime level control. A more in-depth look using data on the insulin-to-carbohydrate or basal-to-bolus ratios could be used to understand fully the results from the group of women using insulin pumps. With the women who had LGA infants, researchers were able to find actual periods of high glucose levels as early as the first trimester from their data. This evidence infers that the length of time exposed to even the smallest excess of glucose is essential to manage for better fetal growth outcomes.  

A weakness of the study was interstitial glucose, potentially not reflecting the real levels of blood glucose. In situations of hypoglycemia and even rapid blood glucose changes, the quality of the readings could have been reduced. Another weakness was the lack of dietary information on meal and snack times. Due to this, researchers could not account for sure if dietary intake increased blood glucose levels during the day.  

In all, researchers suggest replacing fast-absorbing carbohydrate-rich meals with more slowly absorbed ones, increasing postprandial physical activity to ensure better peripheral glucose uptake, and to administer bolus insulin 15 minutes before the meal to help keep blood glucose levels in range.  

Practice Pearls: 

  • Expecting mothers with type 1 diabetes who use RT-CGM experience lower blood glucose levels than women who use SMBG. 
  • Further studies looking at insulin-to-carbohydrate or basal-to-bolus ratios could better explain why women who used insulin pumps only had glycemic control during the first trimester. 
  • Women who had LGA infants had higher blood glucose levels; this implies that length of time being out of the desired blood glucose range could affect fetal growth. 
  • Recommendations on how to keep blood glucose levels in-range include using more slowly absorbed carbohydrates, increasing postprandial physical activity, and to administer bolus insulin 15 minutes before the meal. 

Scott, Eleanor M., et al. “Continuous Glucose Monitoring in Pregnancy: Importance of Analyzing Temporal Profiles to Understand Clinical Outcomes.” Diabetes Care, vol. 43, no. 6, 2020, pp. 1178– 1184., doi:10.2337/dc19-2527. 

Scholtens, Denise M., et al. “Hyperglycemia and Adverse Pregnancy Outcome Follow-up Study (HAPO FUS): Maternal Glycemia and Childhood Glucose Metabolism.” Diabetes Care, vol. 42, no. 3, 2019, pp. 381–392., doi:10.2337/dc18-2021. 


Maya Palmer, PharmD. Candidate, Florida A&M University College of Pharmacy 


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