Association between maternal exposure to air pollution before conception and sex determination in the city of São Paulo

It has been widely demonstrated that air pollution can affect human health and that some pollutant gases can have negative impacts on female fertility rates and cause adverse obstetric outcomes, such as premature birth and low birth weight. Few studies have evaluated the impact of maternal exposure to urban air pollution on the number of female births. To evaluate the association between maternal exposure to air pollution during the year before conception and sex determination. This was a prospective study using low-risk pregnant women living in Sao Paulo, Brazil. The pollutants were measured by a fixed station during a 1-year period before conception. Sex was confirmed after birth. We used multiple logistic regression models to evaluate the association between the pollutants and the sex determination and to estimate the odds ratio (OR) and the 95% confidence interval (CI) of being female based on a quantitative increase in pollutant concentration. We evaluated 371 patients. Elevated exposure to nitrogen dioxide (NO2) and particulate matter lower than 10 μm (PM10) prior to conception were associated with increased odds of being female. Each unit increase of NO2 exposure increased the odds of being female by 8% (OR = 1.08, 95% CI = 1.02, 1.15, p = 0.008), and each unit increase of PM10 increased the odds of being female by 14% (OR = 1.14, 95% CI 1.02 to 1.28, p = 0.021). In Sao Paulo, maternal exposure to pollutants was significantly associated with the odds of being female.