Five-minute Apgar score and risk of neonatal mortality, severe neurological morbidity and severe non-neurological morbidity in term infants - an Australian population-based cohort study

Background: The aim of this study was to ascertain risks of neonatal mortality, severe neurological morbidity and severe non-neurological morbidity related to the 5-min Apgar score in early term (37(+0)-38(+6) weeks), full term (39(+0)-40(+6) weeks), late term (41(+0)-41(+6) weeks), and post term (>= 42(+0) weeks) infants. Methods: This was a retrospective cohort study of 941,221 term singleton births between 2000 and 2018 in Queensland, Australia. Apgar scores at 5-min were categorized into five groups: Apgar 0 or 1, 2 or 3, 4-6, 7 or 8 and 9 or 10. Gestational age was stratified into 4 groups: Early term, full term, late term and post term. Three specific neonatal study outcomes were considered: 1) Neonatal mortality 2) Severe neurological morbidity and 3) Severe non-neurological morbidity. Poisson multivariable regression models were used to determine relative risk ratios for the effect of gestational age and Apgar scores on these severe neonatal outcomes. We hypothesized that a low Apgar score of <4 was significantly associated with increased risks of neonatal mortality, severe neurological morbidity and severe non-neurological morbidity. Findings: Of the study cohort, 0.04% (345/941,221) were neonatal deaths, 0.70% (6627/941,221) were infants with severe neurological morbidity and 4.3% (40,693/941,221) had severe non-neurological morbidity. Infants with Apgar score <4 were more likely to birth at late term and post term gestations and have birthweights <3rd and <10th percentiles. The adjusted relative risk ratios (aRRR) for neonatal mortality and severe neurological morbidity were highest in the Apgar 0 or 1 cohort. For infants in the Apgar 0 or 1 group, neonatal mortality increased incrementally with advancing term gestation: early term (aRRR 860.16, 95% CI 560.96, 1318.94, p < 0.001); full term (aRRR 1835.77, 95% CI 1279.48, 2633.91, p < 0.001); late term (aRRR 1693.61, 95% CI 859.65, 3336.6, p < 0.001) and post term (aRRR 2231.59, 95% CI 272.23, 18293.07, p < 0.001) whilst severe neurological morbidity decreased as gestation progressed: early term (aRRR 158.48, 95% CI 118.74, 211.51, p < 0.001); full term (aRRR 112.99, 95% CI 90.56, 140.98, p < 0.001); late term (aRRR 87.94, 95% CI 67.09, 115.27, p < 0.001) and post term (aRRR 52.07, 95% CI 15.17, 178.70, p < 0.001). Severe non-neurological morbidity was greatest in the full term, Apgar 2-3 cohort (aRRR 7.36, 95% CI 6.2, 8.74, p < 0.001). Interpretation: A 5-min Apgar score of <4 was prognostic of neonatal mortality, severe neurological morbidity, and severe non-neurological morbidity in infants born >37 weeks' gestation with the risk greatest in the early term cohort.