Job Market Paper
Heatwaves and Health at Birth
This paper studies the impact of prenatal exposure to extreme heat on birth outcomes in Spain. I link over 460,000 administrative birth records from 2012–2021 to high-resolution daily temperature data at the municipality level to construct trimester-specific measures of in-utero heat exposure. Heatwaves are defined as at least three consecutive days with maximum temperatures above the municipality-specific 95th percentile of the historical distribution, with alternative thresholds used for robustness. In contrast to most of the existing literature, I find that exposure to heatwaves during pregnancy—particularly in the third trimester—increases birth weight and gestational age, and modestly raises the probability of cesarean delivery. These results are robust across alternative definitions of extreme heat, model specifications, and functional forms. The findings suggest that in the Spanish context, moderate heat exposure may stimulate fetal growth through behavioral or medical adaptations, highlighting the importance of understanding local resilience and adaptation in the face of a warming climate.