Maternal prepregnancy BMI and child cognition: a longitudinal cohort study.

OBJECTIVE: To examine the association between maternal prepregnancy BMI and cognitive performance in children at 5 and 7 years of age. METHODS: This is a secondary analysis of data from the Millennium Cohort Study, a prospective population based cohort of 19,517 children in the United Kingdom. Standardized cognitive assessments of children, involving components of the British Ability Scales, second edition and a number skills test, were performed at 5 and 7 years of age. Principal components analysis was used to identify a general cognitive ability factor (g) from individual test scores. Maternal prepregnancy BMI was retrospectively self-reported when children were 9 months old. Mixed-effects linear regression models were fitted, controlling for multiple socio-demographic factors, child's birth weight, child's BMI, maternal smoking, and maternal diabetes. Complete data were available for 11,025 children at 5 years, and 9882 children at 7 years. RESULTS: Maternal prepregnancy BMI was negatively associated with children's cognitive performance (g) at age 5 (P = .0069) and age 7 (P < .0001). The overall effect size was modest: a 10-point increase in maternal BMI was associated with a decrease in cognitive performance of ~1/10th of an SD at age 7. CONCLUSIONS: Maternal prepregnancy BMI is negatively associated with children's cognitive performance, even after adjusting for multiple socio-demographic confounders and children's BMI. The relationship appears to become stronger as children get older, although the overall effect size is modest. In utero fetal programming or residual confounding may explain these findings.