The Effects of Birth Weight on Hospitalizations and Sickness Absences

This study examines the causal effects of birth weight on two health-related outcomes: inpatient hospitalizations and sickness absences, distinguishing between different diagnoses. Our analysis exploits differences within siblings and within twin pairs, using full population Swedish register data on cohorts born between 1973 and 1995, observed through childhood and in adulthood. In childhood, there is a strong relationship between birth weight and days in inpatient care. This is mostly driven by perinatal conditions during infancy, but substantial effects on other conditions are also found. Effects reduce in size when the child grows older. There are also significant and important effects in adulthood, and these are stronger than the ones found in late childhood. In adulthood, the strongest and most consistent effects are obtained for mental conditions. This holds for both hospital visits and sickness absences, but is most striking for hospital visits, where mental diagnoses may account for almost the entire effect of a lower birth weight. Overall, we provide evidence that birth weight does matter for both short- and long-term health outcomes and that the effects may not be smaller than what more traditional OLS regressions suggest.