Separated at Girth: US Twin Estimates of the Effects of Birth Weight

The fetal origins hypothesis asserts that nutrient deprivation in utero can raise chronic disease risk. Within economics, this hypothesis has gained acceptance as a leading explanation for the correlations between birth weight, a proxy for fetal nutrient intake, and adult outcomes. Exploiting birth-weight differences between twins using (a) a newlycreated dataset of twins from 1960-1982 California birth records and (b) the Early Childhood Longitudinal Study Birth Cohort, I find birth weight is related to educational attainment, later pregnancy complications, and the birth weight of the next generation. These effects are generally small. However, the protective effects of birth weight vary across the birth-weight distribution. (JEL: I12, I21, J13)