Abstract: Racial and ethnic disparities in maternal adverse outcomes remain a significant public health problem. Studies conducted in New York City (NYC) hospitals have shown that minority women are more likely to deliver in low-quality hospitals and that they are also at a higher within-hospital risk of severe maternal morbidity (SMM) than white women, even after accounting for type of insurance. Although these studies represent important pointers in our understanding of SMM disparities, there are still many open questions about how quality of delivery hospitals drives the higher rates in adverse outcomes observed for minority women. First, it is unknown whether racial/ethnic differences in delivery hospital quality (between and within) exist in cities or regions other than NYC, especially in rural areas. Second, there is little information on the reasons for differences in where women of different racial/ethnic status deliver. Third, previous efforts examining racial disparities in healthcare delivery have mainly focused on individual-level factors overlooking the broader macro-level societal and structural conditions (e.g., structural racism) that may be at play. Finally, it is unknown how important policies such as Medicaid expansion have impacted obstetric hospital quality, especially minority- and rural-serving hospitals. Research studies investigating higher level factors that transcend individual-level factors to explain racial/ethnic disparities in maternal outcomes are urgently needed to design effective interventions. Thus, the proposed study will address the following: 1) Determine the contribution of delivery hospital quality to racial/ethnic disparities in maternal mortality and SMM; 2) Examine within-hospital racial/ethnic disparities in risk-adjusted maternal mortality and severe morbidity and identify whether these disparities are associated with types of medical insurance and broader societal and structural conditions; 3) Determine societal- and individual-level maternal factors associated with using versus bypassing high-quality hospitals; 4) Identify the impact of expanded Medicaid income eligibility to adults earning up to 138% federal poverty level on: (Aim 4a) hospital quality (especially safety-net and rural-serving hospitals); and (Aim 4b) the incidence of maternal mortality and SMM, either overall or by race/ethnicity and socioeconomic status. We will use birth certificate data linked to hospital discharge data and supplemented by other datasets from eight U.S. states from 2000-2019 to develop a risk-adjusted maternal mortality and SMM composite outcome which will allow us to rank hospitals. We will subsequently use hospital ranking to examine the contribution of hospital quality to racial/ethnic disparities. The aim on Medicaid expansion will make use of a natural experiment framework and difference-in-difference analysis resulting in comparing each state to itself, before and after Medicaid expansion. At the end of the...