Low birthweight and the risk for mental retardation later in childhood.

Data from the population-based Metropolitan Atlanta Developmental Disabilities Study were used in a case-control study to assess the association between low birthweight and mental retardation (intelligence quotient < or = 70) among 10-year-old children who were born in 1975 or 1976. Children with mental retardation were identified from existing records at multiple sources and control children were selected from public school rosters. Data on birthweight and other covariates (sex, birth order, maternal age, maternal race, maternal education and gestational age) came from birth certificates. We used multiple logistic regression modelling to obtain adjusted odds ratios for mental retardation, with normal birthweight children (those weighing > or = 2500 g) as the referent group. For low birthweight children as a whole, the odds ratio for mental retardation was 2.8 (95% CI 1.9-4.2). The risk was higher for very low birthweight (< 1500 g) children than for moderately low birthweight (1500-2499 g) children, and higher for severe mental retardation (intelligence quotient < 50) than for mild mental retardation (intelligence quotient 50-70). Adding gestational age to the models revealed that normal birthweight children who were born preterm also were at increased risk of having mental retardation at age 10 years.