Body size at birth in babies born during World War II: The evidence from Poland

Objectives The objective of the study was to determine whether exposure of pregnant women to stresses caused by World War II (WWII) negatively affected pregnancy and perinatal outcomes. Methods Individual medical documents deposited in the Gynaecology and Obstetrics Clinic of Medical University, Poznan (1934-1943; N = 7058) were evaluated. These were divided into two birth cohorts: before WWII and during it. Frequency tables were constructed for the numbers of pregnancy outcomes: miscarriages, stillbirths, live births, and neonatal deaths, according to the period of birth and sex of a child. The numbers of recorded days were standardized and the numbers of cases per day were computed. Statistical differences in the averages (medians) between periods and years under study were tested. Birth weight, length, and body mass index (BMI) were compared according to the periods related to WWII. Results Significant differences in proportions of males, females, and subjects with unknown sex were found between the periods: a higher proportion of males and different structure of/within negative outcomes were found during WWII. Children born during WWII were heavier and longer than those born before it. Conclusions As an explanation, adverse conditions of WWII, related to the psychological stress and food shortages, could have influenced greater elimination of fetuses and neonates of male sex during pregnancy and shortly after delivery. Higher average body size in newborns recorded during WWI could be explained by a hidden process of increased early prenatal mortality of weaker individuals, differences in average gestation length between the periods, differences in parity, or some undocumented differences in social/ethnic composition of the sample.