Birthweight and cognitive development during childhood

Objectives: Low birthweight has been reported to be associated with lower IQ at school age. Further, some evidence suggests that the association extends across the range of normal birthweights. This study assessed the relationship of birthweight to cognitive development in the Port Pirie birth cohort. Methods: Of 723 singleton live births recruited into a prospective birth cohort study, 601, 548, 494 and 375 children were followed at ages 2, 4, 7 and 11-13 years, respectively. The children's developmental status was assessed using the Bayley Scales of Infant Development at age 2 years, the McCarthy Scales of Children's Abilities at age 4 years, and the revised Wechsler Intelligence Scale for Children at ages 7 and 11-13 years. The association between birthweight and cognitive function was assessed with multiple linear regression, adjusting for a wide range of possible confounders. Results: The mean birthweight was 3386 g (SD: 517). There was a statistically significant association between birthweight and cognitive performance at age 2 years (adjusted deficit: 0.97 points per 100 g lighter; 95% CI: 0.4-1.5), but the magnitude of this association gradually decreased and became statistically non-significant at later childhood. Conclusions: The relationship between birthweight and cognitive development becomes progressively attenuated at increasing age. At older ages, socioenvironmental factors appear to play an increasingly important part in children's cognitive development.