Overview of the National Infant Mortality Surveillance (NIMS) project

A slowdown in the decline of infant mortality in the United States and a continuing high risk of death among black infants (twice that of white infants) prompted a consortium of Public Health Service agencies, in collaboration with all states, to develop a national data base of linked birth and infant death certificates for the 1980 birth cohort. This project, referred to as National Infant Mortality Surveillance (NIMS), provides neonatal, postneonatal, and infant mortality risks for blacks, whites, and all races in 12 categories of birthweights. Tabulations were requested for infants born in single and multiple deliveries. For single-delivery births, tabulations included birthweight, age at death, race of infant, and each of these characteristics: infant's live-birth order, sex, gestation, type of delivery, and cause of death; and mother's age, education, prenatal care history, and number of prior fetal losses at greater than or equal to 20 weeks' gestation. An estimated 95% of eligible infant deaths were included in the NIMS tabulations. Analyses have focused on various components of infant mortality, including birthweight distribution of live births, neonatal mortality, and postneonatal mortality. The most important predictor for infant survival is birthweight; survival increases exponentially as birthweight increases to its optimal level. The nearly twofold higher risk of infant mortality among blacks than among whites was related to a higher prevalence of low birthweights, to higher mortality risks in the neonatal period for infants with birthweights of greater than or equal to 3,000 g, and to higher mortality during the postneonatal period for all infants, regardless of birthweight. Moreover, the black-white gap persisted for infants with birthweight of greater than or equal to 2,500 g, regardless of other infant or maternal risk factors.