Trends and racial differences in birth weight and related survival

In the past two decades, infant mortality rates in the United States declined in African-American and White populations. Despite this, racial disparities in infant mortality rates have increased and rates of low birth weight deliveries have shown little change. In this study, we examine temporal changes in birth weight distributions, birth weight specific neonatal mortality, and the birth weight threshold for an adverse risk of survival within both racial groups in order to explore the mechanisms for the disparities in infant mortality rates.

Single live births born to South Carolina resident mothers between 1975 and 1994 and considered White or African-American based on the mother's report of maternal race on the birth certificate were selected for investigation. We define the birth weight threshold for adverse survival odds as the birth weight at which 50% or more of infants in the population died within the first month of life.

Despite significant increases in very low birth weight percentages, neonatal mortality rates markedly declined. Birth weight specific neonatal mortality decreased for both races, although greater reductions accrued to White low birth weight infants. By the end of the study period, the birth weight at which over 50% of newborns died within the first month of life was 696 g for Whites and 673 g for African-Americans.

The ongoing decline in neonatal mortality is mainly due to reductions in birth weight specific neonatal mortality, probably related to high-risk obstetric and neonatal care. Technological developments in these areas may have differentially benefited Whites, resulting in an increasing racial disparity in mortality rates. Moreover, the relatively greater and increasing mortality risk from postmaturity and macrosomia in infants of African-America mothers may further exacerbate the racial gap in infant mortality.