Uncommon sex ratio at birth during the Second World War: evidence from Poland

This study analyses the evolution of sex ratios at birth in the Polish city of Poznań during World War II. The analysis is based on a sample of over 13,500 unique observations from 1935 to 1944, sourced from the Gynaecology and Obstetrics Clinic of the Medical University of Poznań. Logit regressions were applied to explore the relationship between the probability of a baby being male and various explanatory variables: years before and during WWII, maternal marital status, place of residence, occupation (either the mother’s or her husband’s), maternal age at delivery, and the number of previous deliveries. The findings indicate that during WWII, more boys were born alive than girls, compared to the years preceding the conflict. Among the variables examined, only birth order had a significant impact on sex ratios at birth. Additionally, the study suggests that gestational age may have played a crucial role during WWII, contributing to the higher number of live-born boys compared to girls, as pregnancies tended to end pre-term during the war. This research contributes to the ongoing exploration of sex ratios at birth under acute environmental conditions and highlights those severe conditions experienced by pregnant mothers during WWII adversely affected pregnancy outcomes.