Abstract The COVID-19 pandemic provides an unprecedented opportunity to conduct prospective, longitudinal investigation of the effects of Social Determinants of Health (SDoH), including Structural Racism and Discrimination (SRD), and maternal stress on maternal physical and mental health morbidity. The Stony Brook COVID-19 Pregnancy Experiences (SB-COPE) Study, which forms the foundation for the proposed project, includes detailed prospective psychosocial data from over 7,400 persons who were pregnant at the beginning of the COVID-19 pandemic (n=4,400) or at the second U.S. COVID-19 surge (n=3,000), including 1,400 persons of color. The main objectives of this Urgent Competitive Revision proposal are to prospectively determine pandemic-related impacts on maternal stress, identify SDoH mechanisms associated with these impacts, and investigate the effects of stress on maternal morbidity and perinatal outcomes. The proposal seeks to extend assessment of the SB-COPE Study cohort for an additional year, and to follow participants into the first year postpartum, including, for some, into their next pregnancy. The proposed project will: Aim 1) Identify contributors to maternal stress during the pandemic. It is hypothesized that pregnant persons affected by SDoH, including SRD, will experience more stress as a result of the pandemic. SDoH to be investigated in the pandemic context include geographical disparities, race/ethnicity, relationship and economic status, and sexual and gender identity. SRD factors include prenatal gendered racism, everyday discrimination, and discrimination in healthcare. Stress factors include global perceived stress, pandemic- related stress, pregnancy-specific stress, and stressful life events. Aim 2) Identify contributors to prenatal and postpartum mental health morbidities during the pandemic. Persons with higher levels of stress are hypothesized to report greater mental health morbidities (depression, anxiety, and obsessive-compulsive symptoms) prenatally and in the postpartum period. Differential effects of stress types (e.g., pandemic-related stress, stressful life events) and interactions among stress, SDoH, and SRD (including healthcare access and quality) in predicting mental health outcomes will be examined. Aim 3) Identify pathways resulting in poorer maternal physical health and adverse perinatal outcomes during the pandemic. It is hypothesized that SDoH will predict greater likelihood of adverse perinatal outcomes (e.g., low birthweight, preterm birth; emergency delivery). This association is predicted to be mediated by prenatal maternal stress, maternal health behaviors, and healthcare access and quality. This critically timed project capitalizes on an existing, extensive baseline dataset (including NIH common data elements), large SB-COPE Study cohorts pregnant during critical pandemic periods, including a sizeable number of persons of color, and the highly relevant expertise of a multidisciplinary research tea...