Decomposition of Black and White Infant Mortality Rates.

Importance: The infant mortality rate (IMR) of the non-Hispanic Black population in the US remains more than twice that of the non-Hispanic White population. Understanding this disparity in terms of differences in gestational age distribution, mortality risk within gestational age categories, and specific causes of death is essential for targeting interventions. Objective: To decompose the Black and White infant mortality gap into gestational age composition and mortality risk components and to identify the causes of death that may be factors in recent changes. Design, Setting, and Participants: This cross-sectional study analyzed Period Linked Birth/Infant Death Records from the US National Center for Health Statistics from January 1, 2003, through December 31, 2024. Participants included all live births to non-Hispanic Black mothers and non-Hispanic White mothers with known gestational age and plausible birth weight for gestational age. Exposures: Maternal race and ethnicity of non-Hispanic Black or non-Hispanic White. Main Outcomes and Measures: The primary measures were the composition effect (differences in gestational age distribution) and rate effect (differences in within-gestational age mortality) from a Kitagawa decomposition of the mortality difference between infants born to Black and to White mothers, overall and by specific cause of death. Results: There were 57 870 726 live births and 336 384 infant deaths in the non-Hispanic Black (141 651 [38.7%] of all deaths) and non-Hispanic White (224 733 [61.2%] of all deaths) populations between 2003 and 2024. The Black IMR declined from 13.2 (95% CI, 12.9-13.5) to 10.7 (95% CI, 10.5-11.0) deaths per 1000 live births between 2003 and 2024, while the White IMR declined from 5.6 (95% CI, 5.5-5.7) to 4.3 (95% CI, 4.2-4.4) deaths per 1000 live births. The absolute gap decreased from 7.7 to 6.0 deaths per 1000 live births between 2003 and 2019, but then increased to 6.4 (95% CI, 6.1-6.8) deaths per 1000 live births. The gestational age composition effect accounted for a majority of the difference across study years, but the rate effect increased as a share of the gap from 21% (95% CI, 18%-24%) in 2003 to 32% (95% CI, 28%-35%) in 2024. Between 2020 and 2024, the share of sudden unexpected infant death (SUID) to the gap showed the largest increase of any single cause (0.18 deaths per 1000 live births; SUID gap in 2024, 1.56 [95% CI, 1.42-1.71] deaths per 1000 live births). Conclusions and Relevance: In this cross-sectional study of IMRs, gestational age composition differences accounted for the largest share of the Black and White infant mortality gap. However, the increased share of the mortality risk component over time underscores the need for targeted interventions beyond preterm birth prevention.