Socioeconomic differentials and neonatal mortality: racial comparison of California singletons.

The median family income of the zip code of maternal residence was used to estimate the presence and determine the extent of socioeconomic differentials in the neonatal mortality rates of a cohort of 401,399 white and of 66,577 black Californian singletons born from 1982 to 1983. The neonatal mortality rate in the white infants increased from 3.99 in mothers residing in zip codes with a median family income greater than $25,000 to 12.1 for mothers residing in zip codes with a median family income less than $11,000. With decreasing socioeconomic status there was also a significant increase in the percentage of white infants weighing less than 2,500 g (percentage of low birth weight increased from 3.75 to 8.33) and weighing less than 1,500 g (percentage of very low birth weight increased from 0.56 to 1.46). When the source of the socioeconomic difference in white neonatal mortality was partitioned, 77.4% was due to deterioration in the birth weight distribution and 22.6% to deterioration in the birth weight-specific mortality rates. For the black cohort, the neonatal mortality rate increased from 5.9 in the most, to 9.0 in the least affluent strata. Although decreasing residential median family income was associated with an increase in the percent low birth weight (8.19 v 12.86), the percentage of very low birth weight was not significantly different (1.59 v 2.10). When the source of the differential in black neonatal mortality was partitioned, only 29% was due to deterioration of the birth weight distribution, whereas 71% was secondary to less favorable birth weight-specific mortality rates.(ABSTRACT TRUNCATED AT 250 WORDS)