Continuous Glucose Monitoring, Glycemic Variability, and Excessive Fetal Growth in Pregnancies Complicated by Type 1 Diabetes

Background: To examine trimester-specific associations among glycemic variability, fetal growth, and birthweight in pregnancies with type 1 diabetes mellitus (Type 1 DM). Methods: In this retrospective cohort study of 41 pregnant women with Type 1 DM, we used continuous glucose monitoring (CGM) data to calculate glycemic variability (coefficient of variation of glucose) over a 7-day interval in each trimester. Clinical data, including fetal biometry, birthweight, and perinatal complications, were extracted from medical records. Results: Women maintained good glycemic control during pregnancy, with mean HbA1c in the first, second, and third trimester 6.5%, 6.1%, and 6.4%, respectively. Sixty-three percent of infants were large for gestational age (LGA). Estimated fetal weight percentile (EFW%ile) and abdominal circumference percentile (AC%ile) increased during pregnancy, consistent with accelerated prenatal growth. Correlations between trimester-specific glycemic variability and EFW, AC, and birthweight were not statistically significant. After maternal age adjustment, glycemic variability was not associated with birthweight for any trimester (adj. for first trimester: -38.46, 95% CI: -98.58 to 21.66; adj. for second trimester: -12.20, 95% CI: -51.47 to 27.06; adj. for third trimester: -26.26, 95% CI: -79.52 to 27.00). Conclusions: The occurrence of LGA remains very high in contemporary U.S. women with Type 1 DM, despite the use of CGM and overall good glycemic control. Neither HbA1c nor glycemic variability predicted fetal overgrowth or birthweight. Since LGA is a key driver of maternal and newborn complications in pregnancies with Type 1 DM, our data emphasize the importance of investigating both glucose-dependent and glucose-independent underlying mechanisms.