Association Between the Social Vulnerability Index and Adverse Pregnancy Outcomes.

Objective: To assess the association between the Social Vulnerability Index (SVI) and racial disparities in pregnancy outcomes across U.S. counties and to quantify these racial disparities.

Methods: This was a cross-sectional study using restricted Centers for Disease Control and Prevention data sets, including natality data sets, fetal death data sets, and all-cause mortality data sets from 2016 to 2021. We limited analyses to Black or White individuals aged 15-44 years from 3,114 U.S. counties. Participants were categorized into quartiles based on county-level SVI. The primary outcome was maternal mortality rate while pregnant or within 42 days of the end of pregnancy, and secondary outcomes were pregnancy-related mortality while pregnant or within 365 days of the end of pregnancy, stillbirth, and preterm birth. Mixed-effect generalized linear models with negative binomial distribution were used to quantify disparities, using difference-in-difference analysis to measure the difference in outcomes between Black and White individuals across different levels of social vulnerability (first quartile as referent).

Results: A total of 20,189,328 individuals were included, distributed across SVI quartiles as follows: first quartile 2,558,131, second quartile 4,945,774, third quartile 6,827,503, and fourth quartile 5,857,920. Black individuals experienced significantly higher rates of maternal mortality, pregnancy-related mortality, stillbirth, and preterm birth compared with White individuals regardless of SVI quartiles. Difference-in-difference analyses demonstrated that disparities in maternal mortality rate were significantly larger in the second, third, and fourth quartiles compared with the first quartile (difference-in-difference 14.22 [95% CI, 2.11-26.33], 12.53 [95% CI, 1.26-23.81], and 18.82 [95% CI, 6.67-30.98], respectively). A worsening disparity in pregnancy-related mortality was observed in the fourth quartile, whereas disparities in stillbirth and preterm birth did not show significant differences across SVI quartiles.

Conclusion: Racial disparities in maternal mortality intensified in counties with higher social vulnerability. These findings underscore the need for targeted interventions to address social determinants of health.