PROJECT SUMMARY Maternal health in the US is in crisis, where low-income pregnant and postpartum people (PPP) and PPP of color experience suboptimal quality of care across the prenatal, delivery, and postpartum periods. As the largest payer of maternity care, covering 66% of Black births and 60% of Hispanic births, the Medicaid program plays a critical role in shaping maternal health for lower-income PPP of color, with significant opportunity for care delivery models such as Accountable Care Organizations (ACOs) to improve PPP’s outcomes and equity at scale through improved care integration, coordination, and quality improvement incentives. Despite growing state interest in Medicaid ACOs, empirical evidence on the effects of Medicaid ACOs and ACO model types on PPP is very limited. Yet, identifying optimal ACO model designs is critical for the 35 states that have not yet implemented Medicaid ACOs and for other states looking to reform their ACOs. This R01 will fill these gaps by evaluating the innovative, statewide Massachusetts (MA) Medicaid ACO, which aims to integrate medical, behavioral, and social services and improve care quality and coordination across 16 ACOs under two distinct ACO model types: (1) a primary care physician (PCP)-led ACO, where specialists (e.g., OB/GYNs) are not part of the ACO and (2) a health system and Medicaid managed care plan partnership ACO, where PCPs and specialists are part of the ACO. As patients do not select into a Medicaid ACO or model type, this creates a novel nested natural experiment, which we will leverage in combination with qualitative methods, to examine how Medicaid ACO programs affect health care quality and equity for PPP. Specific aims are to (1) evaluate the effect of MA’s Medicaid ACO program on quality of care-sensitive measures for PPP, including prenatal measures, delivery-related measures, and postpartum measures, using a difference-in-differences approach with claims data, where sub-analyses will examine differential effects by racial/ethnic zip code group, (2) evaluate the effect of PCP-led vs. health system partnership Medicaid ACO models on PPP, using the same outcomes and analytic approach as in Aim 1, and (3) assess how efforts to address maternal health outcomes are being operationalized and prioritized within MA Medicaid ACOs, and how this varies by model type, by conducting semi-structured interviews with clinicians, care coordinators, and leadership; interviews will further capture successes and challenges of these efforts, different organizational programs used to improve maternal health care and equity for the ACO, and how inclusion or exclusion of OB/GYNs and specialists from the ACO affects care management and coordination for PPP. As more states and Medicaid providers implement ACOs, little evidence is available to guide them. Understanding how Medicaid ACOs can improve quality of care for one of their most vulnerable populations—PPP—through value-based care is imperative bot...