Association between fine particulate matter (PM_2.5) air pollution and sex ratio at birth in Taiwan

Sex ratio at birth (SRB) is a simple, noninvasive way to monitor the reproductive health of a population. Sex ratio at birth tends to vary across regions and time periods and has been declining globally over the last 50 years possibly due to exposure to environmental toxins, including endocrine-disrupting chemicals (EDCs) and other pollutants. The findings of few studies that assessed the relationship between ambient air pollution and SRBs have been inconsistent. The aim of this study was to investigate the possible association between long-term exposure to ambient PM_2.5 and number of SRBs across 66 municipalities in Taiwan. Our data on annual numbers of male and female births were obtained from Taiwan's Department of Household Registration, Ministry of Interior Affairs, while PM_2.5 data were obtained from Taiwan's Environmental Protection Administration (TEPA). Mean PM_2.5 levels and number of SRBs were calculated for each municipality from 2010 to 2023. The municipalities were categorized into PM_2.5 tertiles (low, medium, and high levels) and the relationship assessed between these tertile levels and number of SRB using a linear logistic regression model. Compared to the lowest PM_2.5 level, the adjusted ORs for the middle and the highest tertile of PM_2.5 levels were 1.015 (1.006-1.024) and 1.018 (1.008-1.029), respectively, noting a significant trend linking increased number of SRBs with higher PM_2.5 levels. This finding is inconsistent with the known fact that male fetuses are more susceptible to environmental threats compared to female fetuses.