Pregnant women from socioeconomically disadvantaged populations living in tropical climates are most vulnerable to the effects of climate change. Extreme heat has been linked to preterm birth, fetal growth restriction, stillbirth and preeclampsia. We aim to describe how extreme heat leads to these outcomes by studying in detail heat exposure and physiological responses in women across India. Our study involves three linked activities. We will use the Garbh-Ini retrospective cohort (10 000 mother-baby pairs) to identify biomarkers and clinical factors associated with heat exposure and adverse outcomes. We will also describe how the fetal heart rate changes with heat exposure by studying a large database of 110 000 antenatal fetal heart traces recorded across India. These findings will inform a prospective, matched cohort study of 600 women vulnerable to heat stress across three different climate zones. Using state-of-the-art climate, imaging and laboratory diagnostics, we will study how heat exposures affect maternal, placental, fetal and lactational function. We will capture women?s lived experiences with heat, identifying opportunities for local heat adaptation. As findings emerge, we will bring together policymakers, researchers, clinicians and people living with heat to develop practical policies and actions that will protect women and their babies.