Project Summary/Abstract Postpartum depression (PPD) is a common and impactful public health problem, which can have severe and lasting consequences for the mother and infant, and sometimes the entire family. The Reach Out, Stand Strong, Essentials for New Mothers (ROSE) program is an evidence-based intervention that prevents half of cases of postpartum depression and was one of two interventions recommended by the US Preventive Services Task Force in 2019. All effectiveness trials of ROSE and of the other recommended PPD prevention intervention included only low-income women a single risk factor that doubles incidence of PPD. Thus, the existing evidence base for PPD prevention consists primarily of women at increased risk for PPD. Based on data from the PIs’ current implementation study of ROSE (R01 MH114883), many healthcare and community agencies in this implementation trial (78%) find it is more feasible for them to provide or offer ROSE to every woman as part of their standard work flow (i.e., provide it as universal prevention), than it is to create a screening and referral process for at risk women (i.e., an indicated or selective prevention approach). In addition to being more feasible for agencies, universal prevention may also be advantageous because the cost of a screening false negative (resulting in a preventable case of PPD; $32,000) far exceeds the cost of ROSE delivery ($50-$300/woman). Effectiveness of ROSE among low-income women at risk for PPD is known (ROSE prevents ~50% of PPD cases). To inform a recommendation about using ROSE as universal vs. selective or indicated prevention, we need to determine the effectiveness of ROSE among general populations of women, including women screening negative for PPD risk (defined in various ways). Thus, this project will assess ROSE effectiveness across PPD risk levels and across prevention approaches in a sample of 2,320 women from a large regional health system (based in Detroit, MI). Each proposed aim gathers a piece of information missing that is needed to guide decision-making about ROSE as universal prevention. We will assess ROSE as universal, selective, and indicated prevention in terms of: (1) ROSE effectiveness relative to a control for each prevention approach in preventing PPD and improving functioning; (2) cost- outcome, (3) equity, and (4) scalability of each prevention approach; and (5) mechanisms of ROSE effects across PPD risk levels. We will integrate results to advise about ROSE as universal prevention. This definitive PPD prevention trial will show how best to get an evidence-based program to those who need it in settings where they receive perinatal care by addressing a pragmatic and novel question (should ROSE be universal prevention?) and by examining equity and cost-outcome of universal vs. other prevention approaches.