Modified Project Summary/Abstract Section The broad, long-term objective of NY-CHAMP's Project 2 is to inform efforts to improve maternal health outcomes by understanding and addressing modifiable risk factors for severe maternal morbidity (SMM) and mortality (MM). Persistent adverse maternal health outcomes are not fully explained by known risk factors. Although social risk factors in the healthcare system are viewed as important contributory causes of health outcomes, few studies have empirically evaluated their role in excess SMM and MM, particularly in high-risk population groups. Evidence regarding effective interventions—at state, county, and hospital levels—to address social risk factors for SMM/MM is even more scant. We propose a rigorous mixed methods project with specific aims to: 1) assess social risk factors at state, county, and hospital levels for SMM, suicidality, and MM; and estimate the hospital costs of SMM/MM attributable to multilevel social risk factors; 2) assess the effectiveness of two program interventions (i.e., Medicaid eligibility generosity and healthcare characteristics) in reducing SMM, suicidality, and MM; and quantify the moderating effects of these two interventions on associations between social risk factors and maternal health outcomes; and 3) analyze the lived experiences of patients and community and hospital stakeholders to identify the mechanisms of, and effective solutions for, social risk factors in maternal health care. We will analyze a robust triangulated set of quantitative and qualitative data from multiple sources, capturing both national and local samples, and apply a complementary suite of multilevel modeling, causal inference, and grounded theory research techniques. Data from the Healthcare Cost and Utilization Project, which provides information on 10 million childbirths from over 1200 hospitals in 21 states during 2016-2022 (Aims 1-2), will be complemented by prospective in-depth interview and focus group data from multisector stakeholders (patients, community, hospital) in three New York City hospital sites (Brooklyn, Washington Heights, Queens) of focus for NY-CHAMP's Intervention Project 2. Aims 1 and 2 will test the hypotheses that: 1) multidimensional indexes of social risk factors are associated with significantly increased SMM, suicidality, and MM; 2) higher state Medicaid eligibility generosity and greater variation in healthcare characteristics are independently associated with lower risks of SMM, suicidality, and MM; and 3) Medicaid eligibility generosity and healthcare workforce characteristics independently mitigate the impact of social risk factors on maternal health outcomes. Aim 3 will be hypothesis generating. Findings will help close important gaps in our understanding of the role that social risk factors play in SMM/MM and generate urgently needed evidence for informing program interventions to improve maternal health outcomes in our city, state, and across the country.