Impact of neonatal growth on IQ and behavior at early school age.

OBJECTIVES The objective was to examine associations of neonatal weight gain (NWG) and head circumference gain (HCG) with IQ scores and behavior at early school age. METHODS We used data from the Promotion of Breastfeeding Intervention Trial, involving Belarusian infants born full term and weighing ≥2500 g. NWG and HCG were measured as the percentage gain in weight and head circumference over the first 4 weeks relative to birth size. IQ and behavior were measured at 6.5 years of age by using the Wechsler Abbreviated Scales of Intelligence and the Strengths and Difficulties Questionnaire (SDQ), respectively, with SDQ collected from parents and teachers. The associations between the exposures (NWG, HCG) and children's IQ and SDQ were examined by using mixed models to account for clustering of measurements, and adjustment for potentially confounding perinatal and socioeconomic factors. RESULTS Mean NWG was 26% (SD 10%) of birth weight. In fully adjusted models, infants in the highest versus lowest quartile of NWG had 1.5-point (95% confidence interval [CI] 0.8 to 2.2) higher IQ scores (n = 13 840). A weak negative (protective) association between NWG and SDQ total difficulties scores was observed for the teacher-reported (β = -0.39, 95% CI -0.71 to -0.08, n = 12 016), but not the parent-reported (β = -0.12, 95% CI -0.39 to 0.15, n = 13 815), SDQ. Similar associations were observed with HCG and IQ and behavior. CONCLUSIONS Faster gains in weight or head circumference in the 4 weeks after birth may contribute to children's IQ, but reverse causality (brain function affects neonatal growth) cannot be excluded.