PROJECT SUMMARY/ABSTRACT Over 15% of women in the United States are impacted by depression during or after pregnancy. Untreated perinatal depression dramatically impairs maternal quality of life and, in its most extreme form, can lead to suicide which remains a leading contributor to maternal mortality. Despite recognition of its importance, multiple barriers exist in the depression care cascade. One of these barriers is the existing health system structure, wherein obstetric and psychiatric care exists in silos and social determinants of mental health (SDoMH) are not systematically integrated into care plans. Without a synergistic approach to the whole woman, both physically and mentally, screening for depressive symptoms occurs inconsistently. Even when screening occurs and depression is diagnosed, treatment is often not initiated, depressive symptoms are not tracked, and care is not escalated with the goal of symptom remission. This lack in coordinated and personalized care has left thousands of women vulnerable each year in the United States. Moreover, there are significant inequities in perinatal depression care which contribute to the widening racial and ethnic disparities in quality of life, maternal morbidity, and maternal mortality. It is imperative that we identify alternative mechanisms to adequately identify and treat perinatal depression in an equitable manner and incorporate mental healthcare as a component of interventions designed to reduce maternal mortality and severe maternal morbidity. The collaborative care model (CCM), when implemented in the primary care context, leads to improvements in mental health outcomes. However, the perinatal context is unique on the patient, clinician, and systems levels. Thus the perinatal CCM (pCCM) requires its own validation. One small (n=168), randomized trial suggests the pCCM is efficacious in reducing depressive symptoms. Despite these data, pCCM remains rarely utilized due to two existing gaps in the research-to-practice continuum. First, the existing efficacy data lack generalizability needed for broad dissemination. Second, no studies have been published to inform best practices with respect to an implementation strategies package for pCCM, with attention to the unique aspects of the perinatal context. Moreover, while the pCCM is an equity-centered intervention, the persistent disparities observed in pregnancy outcomes and perinatal mental health require an intentional, innovative, inclusive, anti-racist approach that builds upon the traditional equity-centered CCM foundations and centers identification and mitigation of SDoMH. We will leverage existing clinical algorithms and databases developed for an established and successful pCCM to perform a rigorous stepped-wedge cluster-randomized trial to evaluate the effect of an equity-enhanced pCCM [COMPASS-PLUS (Collaborative Care Model for Perinatal Depression Support Services – Population-Level Health Equity-Centered Structural Changes)] o...