Both glycaemic control and insulin dose during pregnancy in women with type 1 diabetes are associated with neonatal anthropometric measures and placental weight

Background: To investigate longitudinal associations of maternal glucose/HbA_1c and insulin dose with birthweight-related outcomes in women with type 1 diabetes. Methods: We performed a cohort study including 473 pregnant women with type 1 diabetes with singleton pregnancies. We investigated maternal self-monitored blood glucose (SMBG, mmol/L), HbA_1c (%, mmol/mol) and insulin dose (IU/kg/day) in the three trimesters as potential independent variables, while adjusting for potential confounders. Outcomes of interest were birthweight, birthweight SD score, neonatal length, weight/length index, ponderal index and placental weight. Multiple linear regression analysis was performed with separate analyses for SMBG and HbA_1c. Results: Maternal glucose and insulin dose were independently associated with birthweight-related outcomes. In the main analysis, in the first trimester most associations were positive for insulin dose, in the second the associations were positive for glucose and inverse for insulin while in the third there were no associations. Most sensitivity analyses produced consistent results. In a sensitivity analysis splitting the first trimester in two periods, positive associations of maternal insulin with birthweight-related outcomes were observed in weeks 0+ to 6+. Conclusions: Early in pregnancy in women with type 1 diabetes, maternal insulin dose is positively associated with birthweight-related outcomes, whereas in the second trimester, a positive association with SMBG emerges and the association with maternal insulin becomes inverse. If confirmed in other cohorts, these results would have implications in the management of women with type 1 diabetes.