PROJECT SUMMARY/ABSTRACT Hypertensive disorders of pregnancy (HDP) are a leading cause of maternal mortality and morbidity in the United States (US). HDP (e.g., preeclampsia) present a cascade of health issues for pregnant persons and fetuses. While HDP are not rare in the US (affecting approximately 1 in 12 women), Black women face unique risks and challenges regarding HDP and pregnancy-related mortality (PRM). HDP are more prevalent among Black than White women. Black women also experience more severe HDP than White women. Further, Black women experience the highest rate of pregnancy-related deaths: 41 vs. 16.7/100,000 births in the overall US. Pregnancy-related racial/ethnic disparities persist over time across age groups and groups with higher levels of education. There is no evidence to suggest that genetic or other inherent differences by race/ethnicity explain these disparities; race/ethnicity instead are suggested to represent an amalgam of individuals' social, cultural, political, and economic experiences throughout the life course. Given that pregnancy is also a critical period in the life course, the psychosocial environment during pregnancy is suggested to impact physiologic pathways involved in obstetric and perinatal health. However, the pathways by which the psychosocial environment influence racial/ethnic differences in maternal health outcomes remain unknown. One explanation for these disparities is the experience of psychosocial stress, evidenced by higher mean allostatic load scores among Black women due to psychosocial stress. Therefore, psychosocial stress in pregnancy is a plausible mediator contributing to racial/ethnic pregnancy disparities. Using a nested case-control design with data from a racially diverse cohort, the NICHD-Nulliparous Mothers To Be Study (nuMoM2b), this proposal will assess whether the effect of self-reported race/ethnicity on HDP is partially mediated by psychosocial stress in pregnancy. This study will also explore if the mediated pathway is moderated by social support during pregnancy. Social support is conjectured to function as a coping mechanism that helps individuals overcome psychosocial stress. Study aims are to (1-2D) examine the total effects of self-reported maternal race/ethnicity and HDP, including the indirect effect through a mediated pathway via psychosocial stress, and (3) evaluate if perceived social support modifies the partially mediated models. This study will go beyond the traditional approach in the literature of describing differences between groups and instead propose that the social construct of race/ethnicity represents the cumulative lived experiences of individuals belonging to a specific racial/ethnic group. Execution of these specific aims will advance the NICHD mission to understand human development, improve reproductive health, enhance the lives of children and adolescents, and optimize abilities for all. Specifically, by elucidating possible causal pathways to reduce...