  This study uses data from the 1918-1920 influenza pandemic in Japan along
with newly digitized and complete census records on births and infant deaths to
analyze mortality selection in utero. 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.
