PROJECT SUMMARY/ABSTRACT The global population is experiencing unprecedented rates of extreme weather events, elevated temperatures, and natural disasters due to climate change, which in turn are compounding effects of environmental exposures in already vulnerable communities, increasing susceptibility, and widening existing health disparities. Mounting evidence suggests that extreme temperatures and heat stress may broadly influence cardiometabolic and mental health outcomes yet, the mechanisms are not well understood. Increasingly, evidence suggests that pregnancy is a vulnerable window of exposure to environmental insults for later maternal health effects. Similarly, pregnant people are considered among the most vulnerable to the effects of climate change and heat stress, as are socially disadvantaged and historically marginalized populations. However, the short and long-term effects of exposure to climate-induced extreme temperatures and heat stress during pregnancy on maternal cardiometabolic and mental health outcomes have not been investigated in depth. We hypothesize that prenatal exposure to heat stress is associated with greater maternal cardiometabolic complications and depressive symptoms both during and after pregnancy. We propose to examine this hypothesis and the following specific aims in 412 maternal participants in the MADRES cohort—a cohort of predominantly low-income Hispanic participants in Los Angeles. Aim 1 will examine whether prenatal exposure to heat stress (wet bulb globe temperature, WGBT) is associated with maternal cardiometabolic pregnancy complications (e.g., gestational hypertension, preeclampsia) and postpartum cardiometabolic health indices (blood pressure, lipid profiles, HbA1c, BMI, waist-to-hip ratio); Aim 2 will examine whether prenatal exposure to heat stress (WGBT) is associated with maternal depression during pregnancy and postpartum depressive symptoms using the Center for Epidemiologic Studies-Depression (CES-D) Scale. Aim 3 will explore whether heat shock proteins (HSPs) are potentially useful biomarkers of heat exposure and biological adaptation to heat stress in early and late pregnancy. Findings from this study will help inform planning efforts and policies aimed at mitigating the impacts of extreme heat in urban areas.