Associations between low Apgar scores and mortality by race in the United States: A cohort study of 6,809,653 infants

Abstract

Background: Apgar scores measure newborn health and are strongly associated with infant outcomes, but their performance has largely been determined in primarily white populations. Given the majority of the global population is not white, we aim to assess whether the association between low Apgar score and mortality in infants varies across racial groups.

Methods and findings: Population-based cohort study using 2016 to 2017 United States National Vital Statistics System data. The study included singleton infants born between 37+0 and 44+6 weeks to mothers over 15 years, without congenital abnormalities. We looked at 3 different mortality outcomes: (1) early neonatal mortality; (2) overall neonatal mortality; and (3) infant mortality. We used logistic regression to assess the association between Apgar score (categorized as low, intermediate, and normal) and each mortality outcome, and adjusted for gestational age, sex, maternal BMI, education, age, previous number of live births, and smoking status, and stratified these models by maternal race group (as self-reported on birth certificates). The cohort consisted of 6,809,653 infants (52.8% non-Hispanic white, 23.7% Hispanic, 13.8% non-Hispanic black, 6.6% non-Hispanic Asian, and 3.1% non-Hispanic other). A total of 6,728,829 (98.8%) infants had normal scores, 63,467 (0.9%) had intermediate scores, and 17,357 (0.3%) had low Apgar scores. Compared to infants with normal scores, low-scoring infants had increased odds of infant mortality. There was strong evidence that this association varied by race (p < 0.001) with adjusted odds ratios (AORs) of 54.4 (95% confidence interval [CI] 49.9 to 59.4) in non-Hispanic white, 70.02 (95% CI 60.8 to 80.7) in Hispanic, 23.3 (95% CI 20.3 to 26.8) in non-Hispanic black, 100.4 (95% CI 74.5 to 135.4) in non-Hispanic Asian, and 26.8 (95% CI 19.8 to 36.3) in non-Hispanic other infants. The main limitation was missing data for some variables, due to using routinely collected data.

Conclusions: The association between Apgar scores and mortality varies across racial groups. Low Apgar scores are associated with mortality across racial groups captured by United States (US) records, but are worse at discriminating infants at risk of mortality for black and non-Hispanic non-Asian infants than for white infants. Apgar scores are useful clinical indicators and epidemiological tools; caution is required regarding racial differences in their applicability.

Fig 1. Flowchart of exclusions from study population to analysis cohort.

¹Exclusion criteria overlapped, these values represent the frequency of cases in the study population, not necessarily the frequency of excluded cases. ²Important variables included maternal race, maternal education, number of prenatal care visits, smoking status, and 5-minute Apgar score.

Fig 2. AORs and 95% CIs for early neonatal, overall neonatal, and infant mortality in relation to Apgar score, stratified by maternal race group (n = 6,809,653).

AORs of (1) early neonatal mortality; (2) overall neonatal mortality; and (3) infant mortality for infants with low (0 to 3) and intermediate (4 to 6) 5-minute Apgar scores referent to infants with normal (7 to 10) 5-minute Apgar scores. ORs were adjusted for infant sex, maternal age, maternal smoking status, infant birth weight, maternal education, maternal BMI, previous number of live births and gestational age. AOR, adjusted odds ratio; CI, confidence interval; Hisp, Hispanic; NHA, non-Hispanic Asian; NHB, non-Hispanic black, NHO, non-Hispanic other; NHW, non-Hispanic white.