Birth weight and cognitive ability in adulthood: A systematic review and meta-analysis

Birth weight is associated with a range of adult health outcomes. In childhood, there is a positive association between birth weight – in the normal range (>2,500 g) – and cognitive ability, but no systematic review has yet assessed this effect across adult life. We aimed to synthesise published studies assessing the relationship between birth weight and general cognitive ability in non-clinical adult populations (≥ 18 years). Nineteen studies (N = 1,122,858), mean participant age ranged from 18 to 78.4 years, fulfilled the inclusion criteria, of which eight could be included in a random-effects meta-analysis. Birth weight was associated with cognitive ability in adulthood, with each kilogram increase in birth weight associated with a 0.13 SD increase in general or fluid intelligence (95% CI [0.07, 0.19]). There was considerable heterogeneity in the effect size (I2 = 97.8%, 95% CI [97.2, 98.4], p < .001). The association was similar after correcting for gestational age and parental social class where data were available. The effect size was larger for participants aged < 60 years than those aged 60 years or over. There is a modest association between birth weight and cognitive ability in adulthood that may diminish at older ages.