Daughters over sons: could physical labor and social stress have shaped birth patterns of single mothers in 19th-century Poznań?

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The study examines the proportion of males to females at birth among unmarried and married mothers in Poznań, Poland, during the nineteenth century. We used individual information on births collected from birth registers of seven Poznań parishes (n = 82,005). The data records contained the following information: child’s sex, parental religion, father’s occupation, and maternal marital status. GAM logistic models were used to analyse the data. The main results demonstrate that the impact of a mother’s marital status on the probability of bearing a daughter was statistically significant (p = 0.004), i.e. there was a smaller probability of married mothers giving birth to daughters compared to unmarried mothers. The effects of other factors were not statistically significant. This result can be explained by single pregnant women being exposed to more stress resulting from poor living conditions, financial problems, loneliness, unemployment, violence, lack of psychosocial support, social instability, and uncertainty of the future than married women. They worked professionally, which involved physical effort and work stress. Psychological pressure related to women’s exposure to social stressors and physical workload may have disturbed the course of pregnancy and resulted in the elimination of weaker male foetuses more often than female foetuses, resulting in a decline in the proportion of boys to girls at birth. It should be noted, however, that the ratio of males to females at birth could also have resulted from other factors – not identified in this study.