Maternal Vulnerability Index and Severe Maternal Morbidity

Importance: Few studies have investigated the association of composite measures of neighborhood social determinants of health with severe maternal morbidity (SMM), and no research has examined this association for indices tailored to maternal health. Objective: To examine the association of scores in the Maternal Vulnerability Index (MVI), a tool developed to measure maternal risk of adverse health outcomes, with SMM. Design, Setting, and Participants: This retrospective, population-based cohort study was conducted in 5 states (2008-2020 for Michigan, Oregon, and South Carolina; 2008-2018 for Pennsylvania; and 2008-2012 for California) among individuals delivering a fetal death or a live birth between 22 and 44 weeks. Analysis was conducted between August and October 2024. Exposure: The MVI, a composite measure of 43 area-level indicators, was categorized into 6 themes encompassing physical, social, and health care environments. MVI score and themes were examined in quartiles (quartile 1 = lowest risk to quartile 4 = highest risk) based on residential zip code tabulation area. Main Outcomes and Measures: SMM during delivery hospitalization and after discharge within 42 days after delivery. Results: Among 6543255 birthing individuals (3568631 ages 25-34 years [54.5%]; 472145 Asian or Pacific Islander [7.2%], 824239 Black [12.6%], 1673917 Hispanic [25.6%], and 3346807 White [51.2%]), there were 1087936 individuals in MVI quartile 1 (16.6%) and 1376658 individuals in MVI quartile 4 (21.0%). A total of 45051 individuals (0.7%) had SMM during delivery hospitalization, while 13534 individuals (0.2%) had SMM after discharge within 42 days after delivery. In adjusted analyses, there were no associations between MVI score or themes and SMM during delivery hospitalization. However, a dose-response association was observed between MVI score and SMM within 42 days after delivery (second MVI quartile: adjusted relative risk [aRR], 1.03; 95% CI, 0.95-1.11; third MVI quartile: aRR, 1.12; 95% CI, 1.03-1.23; fourth MVI quartile: aRR, 1.27; 95% CI, 1.14-1.41). The highest MVI quartile in themes of general health care (aRR, 1.27; 95% CI, 1.14-1.43), physical environment (aRR, 1.33; 95% CI, 1.22-1.46), physical health (aRR, 1.23; 95% CI, 1.12-1.35), reproductive health care (aRR, 1.30; 95% CI, 1.15-1.47), and socioeconomic determinants (aRR, 1.19; 95% CI, 1.02-1.39) was associated with SMM within 42 days after delivery. A dose-response association was observed between all MVI themes and SMM within 42 days after delivery (eg, physical environment MVI theme second quartile: aRR, 1.04; 95% CI, 0.96-1.13; third quartile: aRR, 1.14; 95% CI, 1.05-1.25; fourth quartile: aRR, 1.33; 95% CI, 1.22-1.46), except for the mental health and general health care themes. Conclusions and Relevance: In this study, MVI score was not associated with SMM during delivery but was associated with postpartum SMM, suggesting that MVI may capture long-term risks more effectively than acute conditions during delivery hospitalization.