Postneonatal infant mortality in infants to a neonatal intensive care unit.

The postneonatal infant mortality (PNIM) of 2,205 infants admitted to a neonatal intensive care unit from January 1971 to December 1974 was 44 in 1,000 infants who survived to age 28 days. This rate is approximately ten times that of the general population. Congenital malformations (59%), infections (12%), sudden infant death syndrome (10%), and asphyxial brain damage (10%) were the most common causes of death. One third (26) of the infants remained in the hospital whereas two thirds (52) had been dismissed prior to death. All who remained in the hospital plus 36 who had been dismissed died of severe illnesses that were incompatible with prolonged survival. The remaining PNIM was 10 in 1,000 neonatal survivors. This rate is still twice that of the general population. These deaths occurred in infants who were apparently well at the time of dismissal and subsequent examinations. Sudden infant death syndrome and infections constituted the largest portion of this mortality. Factors contributing to mortality in this group were poor socioeconomic status and low birth weight. Maternal age, race, marital status, and neonatal illnesses including apnea were not significantly related. Factors that appear to be important in the birth of high-risk infants continued to be operative in the postneonatal period, and contribute to a high mortality in apparently normal infants dismissed from the neonatal intensive care unit.