Maternal prepregnancy body mass index and offspring attention-deficit/hyperactivity disorder: a quasi-experimental sibling-comparison, population-based design

Background: High maternal prepregnancy body mass index (BMI) has been associated with increased risk of offspring attention-deficit/hyperactivity disorder (ADHD). However, whether this effect is attributable to maternal or familial level confounds has been little examined. Methods: The present study sought to examine these associations, utilizing data from the medical records of a health care system which treats 350,000 patients annually and a sibling-comparison design in a sample of 4,682 children born to 3,645 mothers. Results: When examining the overall maternal effect, a linear association was observed between maternal prepregnancy BMI and child ADHD [b = 0.04, 95% confidence interval (95% CI) = 0.02–0.06, p =.0003], such that a one-unit (i.e. 1 kg/m²) increase in prepregnancy BMI was associated with a 4% increase in the odds of ADHD (exp b = 1.04). However, when the model was reparameterized to take full advantage of the sibling design to allow for the examination of both maternal and child-specific effects, the child-specific prepregnancy BMI effect was not reliably different from zero (b = −0.08, 95% CI = −0.23 to 0.06, p =.24). In contrast, at the maternal-level, average prepregnancy BMI was a reliably non-zero predictor of child ADHD (b = 0.04, 95% CI = 0.02–0.06, p <.0001) with each one-unit increase in maternal prepregnancy BMI associated with a 4.2% increase in the odds of ADHD (exp b = 1.04, 95% CI = 1.02–1.06). Conclusions: The association between maternal prepregnancy BMI and offspring ADHD may be better accounted for by familial or maternal confounds rather than a direct causal effect of BMI.