The impact of prematurity and low birth weight on the leading cause of infant mortality

Abstract

Listen

Translate article

Despite significant declines in the birth defects-specific infant mortality rate (BD-IMR), birth defects continue to be the leading cause of infant death in the United States, with the 1999 to 2001 average being 1.4 per 1000 live births. During this same time period, rates of low birth weight (LBW; <2500 g) and preterm birth (<37 weeks) were 7.6% and 11.8%, respectively. Because of the overlap among adverse birth outcomes it is important for public health initiatives and medical management to delineate the impact of LBW and preterm births on infant deaths due to birth defects. We conducted a study of U.S. BD-IMRs by birth weight and gestational age, stratified by plurality using data from the National Center for Health Statistics linked birth/infant death file for the years 1999 to 2001 combined. Rates were calculated for subgroups by race or ethnicity, maternal age, and type of anomaly—variables that potentially contribute to the impact of birth weight and gestational age on BD-IMRs. About 60% of infant deaths due to birth defects occurred to LBW infants and about half occurred to preterm infants. BD-IMRs were highest for LBW and preterm births. BD-IMRs increased with increasing plurality. Among LBW and preterm infants, however, these rates decreased with increasing plurality. Among singletons, non-Hispanic black infants (rate of 1.6 per 1000 live births) were more likely than non-Hispanic white (1.3) or Hispanic (1.4) infants to die due to a birth defect; however, non-Hispanic black LBW or preterm infants were less likely than corresponding non-Hispanic whites or Hispanics to die due to a birth defect. These analyses provide important insight into the relationship among fatal birth defects, LBW, and preterm births. Prevention initiatives should consider the overlap in these conditions and their associated risk factors. In addition, an enhanced system of fetal death data in the United States would provide useful additions to our understanding of birth defects infant mortality.