Gestational age is the major determinant of neonatal death (death within the first 28 days of life) in preterm infants. The joint effect of gestational age and Apgar score on the risk of neonatal death is unknown.
Using data from the Swedish Medical Birth Register, we identified 113,300 preterm infants (22 weeks 0 days to 36 weeks 6 days of gestation) born from 1992 through 2016. In analyses stratified according to gestational age (22 to 24 weeks, 25 to 27 weeks, 28 to 31 weeks, 32 to 34 weeks, and 35 or 36 weeks), we estimated adjusted relative risks of neonatal death and absolute rate differences in neonatal mortality (i.e., the excess number of neonatal deaths per 100 births) according to the Apgar scores at 5 and 10 minutes and according to the change in the Apgar score between 5 minutes and 10 minutes. Scores range from 0 to 10, with higher scores indicating a better physical condition of the newborn.
There were 1986 neonatal deaths (1.8%). The incidence of neonatal death ranged from 0.2% (at 36 weeks of gestation) to 76.5% (at 22 weeks of gestation). Lower Apgar scores were associated with higher relative risks of neonatal death and greater absolute rate differences in neonatal mortality in all gestational-age strata. For example, among infants born at 28 to 31 weeks, the adjusted absolute rate differences according to the 5-minute Apgar score, with those who had a score of 9 or 10 serving as the reference group, were 51.7 (95% confidence interval [CI], 38.1 to 65.4) for a score of 0 or 1, 25.5 (95% CI, 18.3 to 32.8) for a score of 2 or 3, 7.1 (95% CI, 5.1 to 9.1) for a score of 4 to 6, and 1.2 (95% CI, 0.5 to 1.9) for a score of 7 or 8. An increase in the Apgar score between 5 minutes and 10 minutes was associated with lower neonatal mortality than a stable Apgar score.
In this study, Apgar scores at 5 and 10 minutes provided prognostic information about neonatal survival among preterm infants across gestational-age strata. (Funded by the Swedish Research Council for Health, Working Life, and Welfare and Karolinska Institutet.).