Apgar score and the risk of cause-specific infant mortality: a population-based cohort study

Background The Apgar score has been used worldwide as an index of early neonatal condition for more than 60 years. With advances in health-care service provision, neonatal resuscitation, and infant care, its present relevance is unclear. The aim of the study was to establish the strength of the relation between Apgar score at 5 min and the risk of neonatal and infant mortality, subdivided by specific causes. Methods We linked routine discharge and mortality data for all births in Scotland, UK between 1992 and 2010. We restricted our analyses to singleton livebirths, in women aged over 10 years, with a gestational age at delivery between 22 and 44 weeks, and excluded deaths due to congenital anomalies or isoimmunisation. We calculated the relative risks (RRs) of neonatal and infant death of neonates with low (0-3) and intermediate (4-6) Apgar scores at 5 min referent to neonates with normal Apgar score (7-10) using binomial log-linear modelling with adjustment for confounders. Analyses were stratified by gestational age at birth because it was a significant effect modifier. Missing covariate data were imputed. Findings Complete data were available for 1 029 207 eligible livebirths. Across all gestational strata, low Apgar score at 5 min was associated with an increased risk of neonatal and infant death. However, the strength of the association (adjusted RR, 95% CI referent to Apgar 7-10) was strongest at term (p<0.0001). A low Apgar (0-3) was associated with an adjusted RR of 359.4 (95% CI 277.3-465.9) for early neonatal death, 30.5 (18.0-51.6) for late neonatal death, and 50.2 (42.8-59.0) for infant death. We noted similar associations of a lower magnitude for intermediate Apgar (4-6). The strongest associations were for deaths attributed to anoxia and low Apgar (0-3) for term infants (RR 961.7, 95% CI 681.3-1357.5) and preterm infants (141.7, 90.1-222.8). No association between Apgar score at 5 min and the risk of sudden infant death syndrome was noted at any gestational age (RR 0.6, 95% CI 0.1-4.6 at term; 1.2, 0.3-4.8 at preterm). Interpretation Low Apgar score at 5 min was strongly associated with the risk of neonatal and infant death. Our findings support its continued usefulness in contemporary practice.