Association of maternal body mass index with intellectual disability risk

The study aimed to investigate the association between maternal body mass index (BMI) in early pregnancy and children's intellectual disability (ID) risk in the absence of chromosomal disorders, neurofibromatosis and tuberous sclerosis, taking adverse birth outcomes, maternal hypertension/diabetes and maternal socioeconomic status into consideration.We conducted a cohort study of singletons without common genetic defects born in Sweden during 1992-2006, and followed them from birth until 31 December 2014 (n=1 186 836). Cox proportional hazards models were used to analyse the association between maternal BMI in early pregnancy and the risk of offspring's ID.The risk of ID was higher in children born to mothers who were underweight (HR=1.21, 95% CI=1.07 to 1.36), overweight (HR=1.28, 95% CI=1.21 to 1.34) or had obesity class I (HR=1.63, 95% CI=1.53 to 1.74), obesity class II (HR=2.08, 95% CI=1.88 to 2.30) and obesity class III (HR=2.31, 95% CI=1.46 to 3.65) than in children born to normal weight mothers. Results remained consistent after excluding children with adverse birth outcome or born to mothers with gestational hypertension/diabetes. Analysis stratified by maternal education and annual household income showed that the association between maternal underweight and children's ID risk was attenuated among children of mothers with tertiary education or with high income.Our findings suggest that maternal underweight or overweight/obesity in early pregnancy was associated with the development of ID in their offspring. This association was independent of the effect of adverse birth outcomes and maternal hypertension/diabetes. High socioeconomic status may attenuate the risk of ID among children of underweight mothers. This study highlights the importance of improving health education before conception to reduce children's ID risk.