Exploring the relationship between maternal Continuous Glucose Monitoring "time in range" and fetal abdominal circumference in pregnant women with Type 1 Diabetes.

Background: To explore the relationship between maternal glycaemic control and fetal abdominal circumference in pregnancies complicated by T1D.

Methods: This is a retrospective cohort study of 81 pregnant women with T1D using CGM. Inclusion criteria were T1D, CGM use, ≥2 in-house ultrasounds, and the birth of a live singleton neonate between 1st December 2019 and 1st December 2022. Linear regression analysis was used to assess the cross-sectional relationships between estimated fetal abdominal circumference (AC) on ultrasound and time in range (TIR) at matched time-points in the third trimester of pregnancy. Linear regression analysis was also used to examine whether first trimester TIR and HbA1c predicts third trimester fetal AC.

Results: At baseline, the mean ± standard deviation (SD) of the first trimester HbA1c was 7.0 ± 1.4% and mean ± SD total daily dose (TDD) insulin was 46.6 ± 21.0 units. The mean ± SD birthweight was 3367.0 ± 861.3 grams. There was no cross-sectional relationship between TIR and fetal AC at 28-, 32- or 36-week' gestation. The results of the regression analysis indicate a significant relationship between first trimester TIR (independent predictor) and fetal AC (dependent variable) at 32- and 36-weeks' gestation while controlling for maternal age, BMI, pump use, and TDD insulin (Adjβ= -0.42, 95%CI -0.80 to -0.03 and Adjβ = -0.57, 95%CI -1.02 to -0.12 at 32- and 36-weeks respectively). Although there was a significant relationship between first trimester HbA1c and fetal AC at 32-weeks' gestation (β = 3.81, 95%CI 0.29 to 7.33), the relationship was not significant after adjustment for confounders.

Conclusions: There was no cross-sectional relationship between TIR and fetal AC in the third trimester of pregnancy but first trimester TIR did predict fetal AC in late pregnancy.