Differences in trends of postneonatal mortality by birthweight in upstate New York, 1968-1979.

Postneonatal mortality among neonatal survivors and the distribution of age at death among infant deaths were examined for births occurring in upstate New York, 1968-1979. Postneonatal mortality rates increased among infants weighing 501-1500 grams. Infants weighing 1501-2000 grams experienced an increase in postneonatal mortality during the mid-1970s, later returning to the level of 1968. Among infants 2001+ grams, postneonatal mortality declined throughout the study period. Among all levels of birthweight, the proportion of infant deaths occurring as postneonatal deaths increased.