Birth weight and cognitive function in the British 1946 birth cohort: longitudinal population based study

Objective To examine the association between birth weight and cognitive fun ction in the normal population. Design A longitudinal, population based, birth cohort study. Participants 3900 males and females born in 1946. Main outcome measures Cognitive function from childhood to middle life (mea sured at ages 8, 11, 15, 26, and 43 years). Results Birth weight was significantly and positively associated with cogni tive ability at age 8 (with an estimated standard deviation score of 0.44 ( 95%, confidence interval 0.28 to 0.59)) between the lowest and highest birt hweight categories after sex, father's social class, mother's education, an d birth order were controlled for. This association was evident across the normal birthweight range (> 2.5 kg) and so was not accounted for exclusivel y by low birth weight The association was also observed at ages 11, 15, and 26, and weakly at age 43, although these associations were dependent on th e association at age 8. Birth weight was also associated with education, wi th those of higher. birth weight more likely to have achieved higher qualif ications, and this effect was accounted for partly by cognitive function at age 8. Conclusions Birth weight was associated with cognitive ability at age 8 in the general population, and in the normal birthweight range. The effect at this age largely explains associations between birth weight and cognitive f unction at subsequent ages. Similarly, the association between birth weight and education was accounted for partly by earlier cognitive scores.