In utero exposure to extreme heat increases neonatal mortality.

Sub-Saharan Africa (SSA) has had the highest neonatal mortality rate in the world for the past few decades. In 2021, 27 infants died within the first month of life for every thousand live births in SSA, accounting for 54% of infant deaths (0-12 months) on the continent. Meanwhile, extreme heat events are occurring with increasingly higher frequency in this region due to climate change, worsening the living and health conditions for already vulnerable populations. Despite the prominence of high neonatal mortality rates and the frequent occurrence of extreme weather events in SSA, it remains unclear whether in-utero exposure to extreme heat is a significant contributing factor. Our research investigates this question using granular data on extreme heat and birth records from 33 African countries drawn from the Demographic and Health Surveys. It collects nationally representative, repeated cross-sectional surveys that assess reproductive and health behaviors across the developing countries every 5 years. Employing a measure of heat that simultaneously accounts for the impact of humidity, we show that a cumulative increase of 150 °C in extreme heat exposure during the 9-month pregnancy period is associated with two additional neonatal deaths per thousand live births. Mothers with lower economic status or limited education experience a more pronounced negative impact from exposure to extreme heat, likely due to reduced prenatal care. Our results are relevant to policymakers aiming to curb the negative impacts of climate change by better targeting the victims of extreme heat and developing effective adaptation strategies.