Age at Death Used to Assess the Effect of Interhospital Transfer of Newborns

In New York City, newborn units classified as level 1 (no intensive care) frequently transfer low-birth-weight infants to units classified as level 3 (complete intensive care), but level 2 units (those with intermediate levels of care) transfer rarely. As deaths occurring in the first hours of life are unlikely to be affected by infant transport services, early (first four hours), late (four hours to 28 days), and overall neonatal death rates were separately examined at each of the three levels of care for singleton live-births weighing 501 to 2,250 g. As previously reported, overall neonatal mortality (adjusted for birth weight, gestational age, sex, and race) for births at level 1 units (163.0/1,000) and level 2 units (168.1/1,000) was similar, and rates for births at level 3 (128.0/1,000) were significantly lower. Mortality up to four hours, and from four hours to 28 days, however, differed between level 1 and level 2 units. Among early deaths, the mortality for level 1 births was 68.0/1,000, significantly higher than both the rate for level 2 births (46.0/1,000) and for level 3 births (40.6/1,000). Between four hours and 28 days, mortality relative to level 3 improved for level 1 births, but worsened for level 2 births. For infants with birth weight 1,251 g, for whom transport rates from level 1 units are highest, mortality in level 1 births was higher than in level 2 births only until 18 hours of life; thereafter, level 2 mortality was higher. These results could not be explained by any of eight additional variables examined in a multivariate model, nor by live birth/fetal death misclassification. Early deaths constituted 30% of neonatal mortality in this population. Thus, infant transport cannot replace maternal selection for place of delivery. However, the excess mortality after four hours seen at level 2 units might be avoided by more frequent referral of sick infants to level 3 services.