The Effect of Maternal Stress on Birth Outcomes: Exploiting a Natural Experiment

Florencia Torche, New York University

A growing literature highlights that in-utero conditions are consequential for individual outcomes throughout the life cycle, but research assessing causal processes is scarce. This paper examines the effect of one such condition– maternal stress – on birthweight. Birthweight is an early outcome shown to affect cognitive, educational, and socioeconomic attainment throughout the individual lifecycle. Using a major earthquake as a natural experiment and a difference-in-difference methodology, I show that maternal stress has a substantial detrimental effect on birthweight. This effect is focused on the first trimester of gestation, and it is mediated by reduced gestational age rather than intra-uterine growth restriction. Several robustness checks reject the hypothesis that the association is driven by unobserved selectivity of mothers. The findings highlight the relevance of understanding the early emergence of unequal opportunity and of investing in maternal wellbeing since the onset of pregnancy.