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

To examine trimester-specific associations among glycemic variability, fetal growth, and birthweight in pregnancies with type 1 diabetes mellitus (Type 1 DM).

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.

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. β for first trimester: -38.46, 95% CI: -98.58 to 21.66; adj. β for second trimester: -12.20, 95% CI: -51.47 to 27.06; adj. β for third trimester: -26.26, 95% CI: -79.52 to 27.00).

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.