Pandemic Influenza and Gender Imbalance: Mortality Selection before Births

This study uses data from the 1918-1920 influenza pandemic in Japan along with newly digitized and complete census records on births, infant deaths, and sex ratios during childhood to analyze mortality selection in utero and its role in the gender imbalance. I find that fetal exposure to the influenza pandemic during the first trimester of the pregnancy decreases the proportion of males at birth. The results from mechanism analysis suggest that this decline in male births is associated with the deterioration of fetal and infant health. This result supports a wide range of existing literature on the long-run adverse effects of pandemic influenza. Analysis of population census data provide evidence suggesting that postnatal influenza exposure has long-term impacts on the gender imbalance among children, thereby implying potential disturbance in the future marriage and labor markets.