A parsimonious explanation for intersecting perinatal mortality curves: understanding the effects of race and of maternal smoking

Abstract

Abstract Background Neonatal mortality rates among black infants are lower than neonatal mortality rates among white infants at birth weights Methods We used data on births in the United States in 1997 after excluding those with a birth weight Results Perinatal mortality rates (calculated per convention) were lower among blacks than whites at lower birth weights and at preterm gestational ages, while blacks had higher mortality rates at higher birth weights and later gestational ages. With the fetuses-at-risk approach, mortality curves did not intersect; blacks had higher mortality rates at all gestational ages. Increases in birth rates and (especially) growth-restriction rates presaged gestational age-dependent increases in perinatal mortality. Similar findings were obtained in comparisons of smokers versus nonsmokers. Conclusions Formulating perinatal risk based on the fetuses-at-risk approach solves the intersecting perinatal mortality curves paradox; blacks have higher perinatal mortality rates than whites and smokers have higher perinatal mortality rates than nonsmokers at all gestational ages and birth weights.