Association between census‐tract Social Vulnerability Index and preterm birth rates

Abstract Importance Preterm birth (PTB) is a leading cause of neonatal morbidity and mortality. Understanding how sociodemographic factors alter the risk of PTB, as quantified by the Social Vulnerability Index (SVI), can guide the development of targeted interventions aimed at reducing PTB rates in economically/socially marginalized groups with increased risk. Objectives This study investigated the association between overall SVI and individual SVI themes on PTB (<37 weeks) and very PTB risk (<32 weeks). Design This was a retrospective study using data from the Study of Outcomes in Mothers and Infants (SOMI) cohort, including California births from 2018 to 2021. Hospital records from the Department of Healthcare Access and Information were linked to birth certificate records. Individual‐level data were merged with the 2020 census‐tract grid and the Centers for Disease Control and Prevention SVI shapefile. SVI and individual SVI themes (socioeconomic status, household characteristics, racial and ethnic minority status, housing type, and transportation) were categorized into quintiles. Statistical analysis was performed between July 1, 2023 and July 15, 2024. Setting Statewide analysis of PTB by census tract in California. Participants Study cohort consisted of singleton births with no major malformations across 9129 census tracts. Exposures The primary exposure was census‐tract SVI. Main outcomes and measures Study outcomes were PTB (<37 weeks’ gestation) and very PTB (<32 weeks). Mixed‐effect logistic regression models adjusted for spatial dependencies and relevant confounders. Results This cross‐sectional study included 1,029,639 singleton births (PTB: 71,591[7.0%]) in California from January 1, 2018 to December 31, 2021. Significant associations were found between PTB and successively higher SVI quintiles compared to Very Low SVI quintile, adjusting for confounders. The highest risk was in the Very High SVI quintile (adjusted odds ratio [aOR], 1.34; 95% confidence interval [CI], [1.30, 1.38]). Increased risks were also seen for very PTB and each SVI theme. Conclusion and relevance In this cross‐sectional study of singleton births in California, there was a significant association between higher SVI and PTB at the census‐tract level. This finding highlighted the potential for SVI and SVI themes to be used as a tool to assess the risk of PTB and guide intervention design in high‐SVI areas.