A comparison of 1960 and 1973--1974 early neonatal mortality in selected states.

Linked birth and infant death records from six states provided the opportunity for comparison of 1960 and 1973--1974 early neonatal mortality rates by weight, maternal age and live birth order. The data were analyzed by fitting linear models to the logarithm of the ratio of 1960 to 1973--1974 early neonatal mortality rates. Although there was substantial variability in these ratios by maternal age and birth order, the ratios were nearly constant for birth weights between 1001 and 4500 gm. The decline in mortality among low birth weight infants (2500 gm or less) accounted for over half of the overall decline in early neonatal mortality. The results obtained here are compared with earlier national studies and possible explanations for the decline are discussed.