Nursery survival for infants of birth weight 500-1500 grams during 1982-1995

To evaluate nursery survival of very low birth weight infants (VLBW) over time, born in the same large inner-city hospital with a predominantly Hispanic population.

All liveborn VLBW infants weighing 500-1500 g at birth were included in four time periods of 2 years' duration during 1982 to 1995. Demographics were collected for the obstetric population. Clinical data were collected including maternal and infant perinatal factors. All infants were assigned a cause of death and infants dying with lethal anomalies were then excluded from further evaluations.

Overall survival improved progressively (p = 0.0001) with dramatic improvement in survival of infants 500-750 g birth weight (BW) in period 4 (1994-1995). The number of lethal anomalies did not increase but accounted for a larger portion of deaths in period 4. Decreases in other causes of death over time reflected changes in perinatal care. Although the mothers were high-risk, none of the maternal factors evaluated showed any consistent effect on infant survival. Improved labor and delivery care was associated with improvement in Apgar scores, a decrease in intracranial hemorrhage/intraventricular hemorrhage as a cause of death and an improvement in survival between the first two periods. In spite of the increase in Cesarean sections for infants of 500-750 g BW and their improved survival in period 4, no clear advantage for Cesarean section could be demonstrated. The marked improvement seen in period 4 was associated with three changes in care: increased use of maternal steroids, administration of surfactant, and the use of newer ventilatory methods including high-frequency oscillatory ventilation. Although female gender has been reported to confer a protective influence for survival, this was not found in the final period. Black mothers comprised only about 2.5% of the total obstetric population but delivered approximately 10% of the VLBW infants. Despite the increased incidence of small for gestational age (SGA) among black infants, there were no differences in survival between blacks and Hispanics. Mean birth weight and gestational age in both survivors and nonsurvivors decreased significantly over the four time periods. In period 4, 50% survival occurred at a birth weight of 600-700 g and a gestational age of 23 weeks.

Nursery survival improved throughout the period of the study from 1982 to 1995 but especially during period 4 (1994-1995). Improved survival was associated with changes in both maternal and infant care. In infants of BW 500-750 g, gestational age rather than birth weight was more closely associated with survival.