Decline in neonatal mortality, 1968 to 1977: better babies or better care?

A state's declining neonatal mortality rate was studied over the decade 1968 to 1977 to determine how much of the decrease resulted from improved risk characteristics in the newborn population. A shift was found over time, mostly among white births, toward higher birth weights and longer gestations. Overall, there was a 19% reduction in the low-birth-weight rate. Considerable improvement in birth weight-specific mortality was also found, especially in babies weighing 1,000 to 2,500 g during the last 5 years of the study. A neonatal risk matrix model was applied to the changes over time to separate the improvement due to shifts in population risk characteristics from that due to better care of the newborn. Thirty-four percent of the decade's decrease in NMR was attributable to changes in the birth weight and gestational age makeup of the newborn population. This "better babies" component was more prominent early in the decade and among the white population.