Nonlinear Decline in the Association between Birth Weight and Cognitive Ability from Infancy to Midlife in a Community Sample of Twins

Objectives: Birth weight is a widely used indicator of prenatal experiences in models of the developmental origins of cognitive ability across the lifespan. Methods: We modeled change in the strength of the association between birth weight and cognitive ability in a sample of twins (n = 1,501; 53.1% female; 91.1% White) followed prospectively from infancy to midlife. Results: The magnitude of the association between birth weight and cognitive ability declined exponentially from infancy (β = .59, p < .05) to midlife (β = .27, p < .05). A 1-kilogram increase in birth weight was associated with an 8.85-point increase in cognitive scores at 3 months and a 4.05-point advantage after about 2.5 years. Biometric regression models revealed that shared environmental factors accounted for the decline in the association between birth weight and cognitive ability. A small, positive within-pair association persisted into midlife. Discussion: Findings support developmental origin models of cognitive ability across the lifespan.