Racial Disparities in Infant Mortality Are Impacted by Gestational Age at Birth

Background: Racial disparities in infant health most often disadvantage non-Hispanic black (NHB) infants. Disparities are driven by numerous biological, socioeconomic, and care practice variables that collectively shape the environments an infant experiences during pregnancy, during birth hospitalization, and after hospital discharge. Disparities in NICU quality of care have been described as one factor contributing to higher morbidity and mortality among NHB infants. However, anecdotal experiences in the NICU suggest that NHB preterm infants have better outcomes than white preterm infants. The impact of gestational age at birth – and subsequent NICU hospitalization – on racial disparities in infant mortality is unknown.

Methods: For this retrospective cohort study, we used population data extracted from the CDC WONDER database for infants born in the United States at 22 to 42 weeks gestational age between 2007 and 2017. Data included number of live births, number of deaths, maternal race, infant sex, gestational age at birth, and chronological age of infant at death. Infant mortality rates (IMR) were defined as the number of deaths per 1,000 live births. Ratios of IMR (rIMR) were calculated using the IMR in white infants as the reference population.

Results: A total of 41,473,167 infants were included. White births were the most common (54%), followed by Hispanic (24%) and NHB births (15%). NHB had the highest rate of preterm birth (17%). rIMR for NHB compared to white infants was 2.07, compared to 0.97 for Hispanic versus white and 0.88 for other races versus white. Males had higher mortality than females within each race and overall. rIMR for NHB males versus white males was 2.04 and for NHB females versus white females was 2.10, approximating the rIMR seen in the overall NHB versus white population. Subgroup analysis by gestational age revealed that as gestational age at birth increased, rIMR for NHB versus white infants increased and diverged from 1.0. Among infants born between 22 0/7 and 27 6/7 weeks, rIMR was 0.96 versus 1.67 for infants born between 37 0/7 and 41 6/7 weeks.

Conclusion: While NHB infants are more likely to die than white infants overall, racial disparity in infant mortality was greatest between term NHB and term white infants. There is no significant racial disparity in mortality between NHB and white infants born between 22 0/7 and 27 6/7 weeks gestational age. NICU hospitalization, which offers an environment with relatively reduced exposure to social determinants of health, may be associated with smaller racial disparities for extremely preterm infants.