Economic stress and birth sex ratios in Finland

Abstract In vertebrates, high maternal stress before conception, around conception, or during pregnancy can skew the sex ratio at birth toward females. Similar evidence is also accumulating in humans where stressful external factors (e.g., natural disasters, disease outbreaks and economic downturns) have been correlated with female-biased birth sex ratios at the population level. However, the findings are still mixed. In this study, we examined whether monthly variation in the Consumer Confidence Indicator (CCI), used as a population-wide stress proxy for economic uncertainty, during the preconception and prenatal periods predict monthly sex ratios of live births and stillbirths in the Finnish population (a total of 1,542,064 live births and 4,836 stillbirths) between October 1996 and December 2024. This period covers major economic upheavals from the past decades in Finland: the aftermath of recession in the early 1990’s, financial crisis in 2008–2009, COVID-19 pandemic in the early 2020’s and Russia’s ongoing war against Ukraine, which began in 2022. The results showed no evidence of an increase in proportion of female births or male stillbirths during the periods of economic stress. These findings might indicate that sex ratios were resilient enough to variations in the economic uncertainty-induced stress in Finland but other explanations cannot be ruled out.