Comparison of HbA1c and Time in Range in the Prediction of Large for Gestational Age in Pregnancies Involving Type 1 Diabetes

Background/Objectives: While satisfactory glycaemic control is possible with specialist care from a diabetologist and modern therapies, women with type 1 diabetes are still subject to poorer obstetric outcomes, even with optimal management. Methods: The analysis comprised a cohort of 55 pregnant patients with type 1 diabetes who attended the Diabetology Outpatient Clinic between 2018 and 2023; all were recruited no later than the first trimester. Qualified patients underwent medical interviews and physical examinations. Insulin pump, continuous glucose monitoring (CGM) system, and postpartum data were collected. Results: The median glycated haemoglobin (HbA1c) at the beginning of pregnancy was 6.1%, with means of 5.9% and 6.0% in the following trimesters. Only 1/3 of the women achieved the recommended HbA1c value throughout pregnancy. The average/median time in range (TIR) in each trimester was ≤70%. Among the women who achieved the recommended TIR target, the infants tended to have lower birth weights but a higher likelihood of jaundice. Almost half of the newborns were large for gestational age (LGA), and a third were macrosomic. The strongest predictor of LGA was a mean blood glucose level > 124 mg/dL in the third trimester, which increased the risk of LGA by almost 12 times. Conclusions: Good diabetes control does not prevent LGA/macrosomia. TIR appears to be a better predictor of obstetric complications, including LGA. A mean glucose level ≥ 124 mg/dL in the third trimester greatly increases the risk of LGA.