Objective: To determine whether higher maternal body mass index (BMI), independent of maternal glycaemia, is associated with adverse pregnancy outcomes.
Design: Observational cohort study.
Setting: Fifteen centres in nine countries.
Population: Eligible pregnant women.
Methods: A 75-g 2-hour oral glucose tolerance test (OGTT) was performed between 24 and 32 weeks of gestation in all participants. Maternal BMI was calculated from height and weight measured at the OGTT. Fetal adiposity was assessed using skinfold measurements and percentage of body fat was calculated. Associations between maternal BMI and pregnancy outcomes were assessed using multiple logistic regression analyses, with adjustment for potential confounders.
Main outcome measures: Predefined primary outcomes were birthweight >90th percentile, primary caesarean section, clinical neonatal hypoglycaemia and cord serum C-peptide >90th percentile. Secondary outcomes included pre-eclampsia, preterm delivery (before 37 weeks) and percentage of body fat >90th percentile.
Results: Among 23 316 blinded participants, with control for maternal glycaemia and other potential confounders, higher maternal BMI was associated (odds ratio [95% confidence interval] for highest {> or =42.0 kg/m(2)} versus lowest {<22.6 kg/m(2)} BMI categories) with increased frequency of birthweight >90th percentile (3.52 [2.48-5.00]) and percentage of body fat >90th percentile (3.28 [2.28-4.71]), caesarean section (2.23 [1.66-2.99]), cord C-peptide >90th percentile (2.33 [1.58-3.43]) and pre-eclampsia (14.14 [9.44-21.17]). Preterm delivery was less frequent with higher BMI (0.48 [0.31-0.74]). Associations with fetal size tended to plateau in the highest maternal BMI categories.
Conclusion: Higher maternal BMI, independent of maternal glycaemia, is strongly associated with increased frequency of pregnancy complications, in particular those related to excess fetal growth and adiposity and to pre-eclampsia.