Mortality and time to death in very low birth weight infants: California, 1987 and 1993

Background. Recent advances in perinatal technology have dramatically incre ased the survival of very low birth weight (VLBW) infants (<1500 g). The po ssibility that these advances may also prolong the time to death and increa se pain and suffering has been of concern, but there have been no populatio n-based evaluations of this issue. Methods. Infant, neonatal, and postneonatal mortality rates and time to dea th for infants 500 to 749 g, 750 to 999 g, 1000 to 1499 g, and all VLBW inf ants born during 1987 were compared with those outcomes for infants born in 1993 using statewide California linked birth/death cohort files. To assess the effects of improved survival and changes in time until death, we calcu lated the total days of life preceding an infant death per 1000 live born i nfants (TDD). Results. VLBW infants comprised .96% of California's live births in 1987 an d .92% of those in 1993. Between 1987 and 1993, VLBW infant mortality rate decreased 28.4% (from 290.7 to 208.3 per 1000 live born VLBW infants), VLBW neonatal mortality rate decreased 30.3% (from 244.5 to 170.4), and VLBW po stneonatal mortality rate decreased 25.3% (from 61.2 to 45.7 per 1000 VLBW alive at 28 days; P < .05 for each rate). Infant mortality rates decreased by 18.8% (718.1 to 583.0 per 1000) for infants 500 to 749 g, 43.3% (375.1 t o 202.6) for infants 750 to 999 g, and 40.1% (127.9 to 76.7) for infants 10 00 to 1449 g (P < .05 for each group). Neonatal mortality and postneonatal mortality rates also decreased in all 3 VLBW subgroups. These reductions in mortality rates were not accompanied by a significant difference in the di stribution of times to death or a significant increase in the average time to death for all VLBW infants (22.0 vs 23.6 days) or for those with birth w eights of 500 to 749 g (12.7 vs 71.5 days). Reduced mortality in larger inf ants was accompanied by an increase in the average time to death, from 24.3 to 32.5 days in infants 750 to 999 g and from 32.3 to 47.0 days in infants 1000 to 1449 g. TDD decreased from 6410 to 4908 days for all VLBW infants. TDD was also reduced 26.4% (2401 days), 24.3% (2115 days), and 22.5% (1043 days) for the 3 VLBW birth weight groups. Conclusions. Both mortality rate and timing of death are important when ass essing the impact of advances in perinatal technology. Although the average time to death was significantly increased in VLBW infants weighing >750 g, between 1987 and 1993, advances in perinatal technology dramatically decre ased VLBW mortality. In the State of California in 1993, this resulted in 4 52 fewer VLBW deaths and 8233 fewer days preceding a VLBW death than expect ed.