Social class indicators and mortality in low birth weight infants.

This study examines the utility of birth weight-specific neonatal mortality rates in removing the confounding effects, in comparisons of mortality in low birth weight infants, of several factors that influence crude neonatal mortality. For this purpose, the effects of social, demographic, and biological attributes of mothers on the mortality of their low birth weight babies were examined in the total population of infants weighing 501-2000 gm born in New York City in 1976, 1977, and the first 11 months of 1978 (N = 10,187). The results confirm previous observations that race, sex, and gestational age-for-weight all exert significant influences on mortality even within narrow (250 gm) birth weight bands. However, mothers' education, number of prenatal visits and whether delivery was on private or ward service, all variables which substantially affect crude neonatal mortality, had no overall effect on weight-specific mortality in the weight range under consideration. Two other socioeconomic indicators, whether delivery was financed by Medicaid, and the marital status of the mother, did significantly affect weight-specific mortality, but their effects were abolished when gestation, race, and sex were entered into the analysis. Although neither maternal age nor parity had any significant individual effects on low birth weight mortality, a linear trend towards lower mortality in older mothers was discovered, and certain age-parity combinations experienced significantly elevated or reduced mortality. In general, weight-specific mortality in low birth weight infants is little influenced by the socioeconomic circumstances of their mothers, particularly when race, sex, and gestation are taken into account. Weight-specific neonatal mortality can therefore be a useful tool in the analysis of the effectiveness of perinatal medical care given to low birth weight infants.