We previously reported that late death (i.e., death after surviving to DOL 84) was higher in black infants compared to non-black infants and in infants whose birth weights were 501-700 g compared to those whose birthweight were greater than 700 g. (Pediatr Res. 1996;39:1549A). The purpose of this study was to identify specific risk factors for late death in extremely premature infants. We reviewed the records of 1844 infants born with gestational age 23-29 weeks and birthweight > 500 g admitted to the Baylor Affiliated Nurseries from 1986 through 1996 who survived to DOL 84. Late mortality in this group was 33/1897 (1.74%).

When initially using univariant modeling, we found significant correlations between late death and decreasing birthweight (p<0.001), male gender(p=0.016), longer duration of oxygen therapy (p<0.001), decreasing gestation (p<0.001), black race (p=0.019), and history of necrotizing enterocolitis (p=0.020). There was no relationship between late death and increasing grade of intraventricular hemorrhage (p=0.8), history of patent ductus arteriosus (p=0.9), lack of antenatal care (p=0.8), or lack of antenatal steroids (p=0.6). When subsequent multivariant logistic analysis was done, however, decreasing birthweight (p=0.016), male gender (p=0.014), longer duration of oxygen therapy (p<0.001), and black race (p=0.037) remained highly correlated with late death, while decreasing gestational age and history of necrotizing enterocolitis did not. Black and white infants in our study had similar birth weights and rates of chronic lung disease, but black infants with chronic lung disease (oxygen use of ≥ 28 days) had a higher risk of late death than did white infants, relative risk 3.2 (95% confidence interval 1.2-8.7).

Just as black race, low birth weight, and gender are important risk factors for early mortality in preterm infants, we conclude that they continue to exert significant influence on neonatal mortality beyond the first 3 postnatal months. We also conclude that the presence of chronic lung disease (as reflected by increasing duration of oxygen therapy) contributes heavily to late death, particularly among black infants. We speculate that future studies that focus on prevention of neonatal death among black infants will need to identify the features that place them at higher risk for early death as well as for late death.