Maternal Nativity, Race, and Ethnicity and Infant Mortality in the US.

Importance: Racial disparities in infant mortality in the US are well-established, but the associations among maternal nativity status, race, ethnicity, and infant mortality remain understudied. Objective: To examine the associations among maternal nativity status and infant mortality by maternal race and ethnicity in the US, and to assess whether these associations differ by gestational age. Design, Setting, and Participants: This retrospective, population-based cohort study used linked birth and infant death records for all recorded US live births from 2016 to 2022. Births to foreign residents and those with missing data on maternal nativity, race, ethnicity, or gestational age were excluded. Exposure: Maternal nativity status (US born vs non-US born). Main Outcomes and Measures: The primary outcome was infant mortality, defined as death within 364 days of life. Logistic regression was used to quantify the association between maternal nativity status and infant mortality, adjusting for maternal and infant characteristics. Leading causes of death among preterm (<37 weeks) and full-term (≥37 weeks) births were examined by nativity. Full-term births were further analyzed by race and ethnicity. Results: Among 25 981 364 births, 20 141 084 (77.5%) were to US-born individuals, and 5 840 280 (22.5%) were to non-US-born individuals (mean [SD] age, 29.1 [5.8] years). US-born individuals had a higher infant mortality rate than non-US-born individuals (5.4 vs 4.0 deaths per 1000 births; adjusted odds ratio [aOR], 1.34; 95% CI, 1.32-1.36). This disparity was primarily seen for full-term births (aOR, 1.58; 95% CI, 1.54-1.63) and was less apparent among preterm births. Among full-term births, higher rates of infant mortality in US-born individuals were found among those identifying as Black (aOR, 1.55; 95% CI, 1.45-1.66), Hispanic (aOR, 1.39; 95% CI, 1.32-1.45), White (aOR, 1.45; 95% CI, 1.35-1.55), and more than 1 race (aOR, 1.33; 95% CI, 1.04-1.69). Leading causes of death differed by nativity and race and ethnicity, with US-born individuals having higher odds of sudden unexpected infant death compared with their non-US-born counterparts among full-term births (aOR, 2.90; 95% CI, 2.74-3.07). Conclusions and Relevance: This population-based cohort study found that US-born individuals had significantly higher odds of infant mortality compared with non-US-born individuals, particularly among full-term births and among those self-identifying as Black, Hispanic, White, or more than 1 race. Sudden unexpected infant death was a major contributor to these disparities. Investigation into the underlying factors contributing to these disparities is needed.