PROJECT SUMMARY Recent policy debates to extend Medicaid postpartum are fueled by the US maternal health crisis: The US maternal mortality rate is the highest among high-income countries and includes stark racial disparities. Black women have a pregnancy-related mortality rate more than 3X higher than White women. Racial and ethnic disparities for maternal morbidity are equally glaring. Immigrants, too, face higher rates of maternal morbidity and perinatal complications. Sustained, continuous access to perinatal health care is critical to maternal health , yet ~45% of women with Medicaid and CHIP lose coverage after 60 days. Postpartum Medicaid extensions are key features of recent policy attempts to address the high Black maternal mortality and morbidity rates. Policymakers need evidence about the impact of postpartum Medicaid access on maternal health outcomes to guide design and implementation. Since March 2020, the Families First Coronavirus Response Act (FFCRA) has conferred a de-facto Medicaid postpartum coverage extension nationwide, but it is due to expire imminently. Meanwhile, 27 states have already adopted or are seeking to pass legislation to extend postpartum Medicaid coverage, but their policy approaches vary in legal basis, eligibility criteria, length of coverage, and immigrant coverage. Moreover, states vary in their existing Medicaid eligibility policies prior to the pandemic, which has profoundly shaped who has remained eligible during the pandemic with uncertain eligibility post-pandemic. Our overarching objective is to evaluate the impact of postpartum Medicaid policy on maternal health outcomes. We propose using an adaptive concurrent mixed-methods design to measure national changes in postpartum Medicaid enrollment while exploiting differences in two states’ policies to examine health care utilization in greater depth. We focus on two large, diverse states: Texas (TX) has expanded Medicaid to six months postpartum through a demonstration waiver, while New York (NY) is using the American Rescue Plan Act to expand Medicaid 12 months postpartum. Using national American Community Survey (ACS) and Medicaid claims data from TX and NY, our quantitative aims will apply interrupted time series (ITS) and difference-in-difference (DID) approaches. In our qualitative aim, we will interview postpartum women, healthcare providers, community-based organizations, and policymakers on the efficacy of postpartum Medicaid extension implementation, which will inform the analysis approach and enrich our findings. Our proposal not only fills gaps in targeted research on the impact of postpartum Medicaid access on maternal health outcomes, but also shifts the paradigm to focus on the “street-level” implementation of policy and its influence onwomen’s access to postpartum benefits. Our findings will be a key resource for policymakers on thedesign and implementation of postpartum Medicaid extension.