Exploring the associations of overweight and obesity with pregnancy outcomes in type 1 and type 2 diabetes: An Australian retrospective cohort study

ABSTRACT Objective To explore the associations of maternal overweight/obesity and pre‐pregnancy body mass index (BMI) on glycemia and pregnancy outcomes in women with pregestational type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). Research Design and Methods We examined prospectively collected data (2010–2019) involving 264 singleton pregnancies affected by pregestational T1DM or T2DM. On separate analyses within each diabetes subtype, pregnancy outcomes were compared across maternal BMI categories and using BMI as a continuous variable. Co‐primary outcomes included preterm delivery, large‐for‐gestational age (LGA) infants, and pre‐eclampsia. Results In those with T1DM (N = 124, 46% overweight or obese), we did not find an association between increasing BMI category and greater risks of pre‐eclampsia, preterm delivery, or LGA infants. However, amongst the women with T1DM, overweight and obesity were associated with higher odds of exceeding the first trimester HbA1c target (6.5%), and each 1 kg/m 2 increase in BMI was associated with higher odds of excess GWG as well as caesarean delivery. In the T2DM cohort (N = 140, 90% overweight or obese), each 1 kg/m 2 increase in BMI above ethnicity‐adjusted normal range was associated with increased odds of pre‐eclampsia (aOR 1.082, 95% CI 1.024 to 1.144) and preterm delivery (aOR 1.042, 95% CI 1.001 to 1.084). In the T2DM cohort, the odds of LGA were numerically higher with each 1 kg/m 2 increase in BMI, but this was no longer statistically significant after adjustment for potential confounders. Conclusions On separate analyses within each diabetes subtype, maternal overweight/obesity was potentially associated with increased odds of pre‐eclampsia and preterm delivery in the T2DM cohort. Amongst those with T1DM, maternal overweight/obesity was associated with non‐attainment of first trimester HbA1c targets. Regression analyses were performed in an exploratory and hypothesis‐generating manner, and larger‐scale studies are required to directly compare the effects of maternal overweight/obesity on pregnancy outcomes in T1DM vs T2DM.