Moderate low birth weight and infectious disease mortality during infancy and childhood.

The purpose of this study was to determine whether moderately low birth weight, singleton babies without congenital anomalies are at increased risk for postperinatal infectious disease mortality. The study cohort consisted of 54,795 live births assembled at 12 medical school-affiliated hospitals in different regions of the United States between 1959 and 1966 and followed prospectively. After exclusions of multiple gestation births, very low birth weight (less than 1,500 g) births, births with major congenital anomalies, and first-week deaths, 51,931 children remained for analysis. Postperinatal infectious disease mortality was assessed through age 7 years. Causes of death were classified independently by two pediatricians, blinded to birth weight status, according to an algorithm developed for the study. Moderately low birth weight infants and children were at increased risk of infectious disease mortality (relative risk (RR) = 2.49, 95% confidence interval (CI) 1.74-3.55). The risk persisted among those whose deaths met our strictest criteria for infectious etiology and was sustained beyond infancy throughout the age interval under analysis. Among those with moderate low birth weight, there was an increased risk among those with preterm birth (RR = 2.77, 95% CI 1.19-6.46) but not among those who were born small-for-gestational age (RR = 1.19, 95% CI 0.37-3.83). The data suggest that moderate low birth weight renders individuals vulnerable to infectious disease mortality during both infancy and childhood. Among moderately low birth weight infants and children, this vulnerability appeared to be attributable primarily to preterm birth rather than to intrauterine growth retardation.