Parental factors in cognitive outcome of non-handicapped low birthweight infants.

A population based cohort of 144 children weighing less than 2000 g who were without major handicap, and a random control sample of 163 children born at term and weighing over 3000 g were investigated. The aim was to assess the relative importance for cognitive development at 5 years of age, of birthweight, parental demographic factors, and factors related to the environment in which the child was reared. The mean non-verbal IQ was 6.1 points lower (95% CI, 2.3 to 10) for the low birthweight (LBW) group, but the difference was reduced to 4.8 points (95% CI, 1.1 to 8.5) after adjusting for confounding parental demographic and childrearing factors. The verbal IQ was similar for the two groups after such adjustment. Paternal education was the main confounding variable, and demographic factors such as parental education and family income were much stronger predictors of child IQ than birthweight or factors related to the childrearing environment. There was no evidence that the cognitive development of low birthweight children was more sensitive to a non-optimal childrearing environment than that of normal birthweight children. These findings indicate that the risk of impaired cognitive development increases with decreasing socioeconomic status, and that this risk is much larger than, and independent of, the small risk attributable to low birthweight.