BackgroundAir pollution is a major health challenge worldwide and has previously been strongly associated with adverse reproductive health. This study aimed to examine the association between spontaneous abortion and seasonal variation of air pollutants in Ulaanbaatar, Mongolia.MethodsMonthly average O3, SO2, NO2, CO, PM10 and PM2.5 levels were measured at Mongolian Government Air Quality Monitoring stations. The medical records of 1219 women admitted to the hospital due to spontaneous abortion between 2009–2011 were examined retrospectively. Fetal deaths per calendar month from January-December, 2011 were counted and correlated with mean monthly levels of various air pollutants by means of regression analysis.ResultsRegression of ambient pollutants against fetal death as a dose–response toxicity curve revealed very strong dose–response correlations for SO2 r > 0.9 (p < 0.001) while similarly strongly significant correlation coefficients were found for NO2 (r > 0.8), CO (r > 0.9), PM10 (r > 0.9) and PM2.5 (r > 0.8), (p < 0.001), indicating a strong correlation between air pollution and decreased fetal wellbeing.ConclusionThe present study identified alarmingly strong statistical correlations between ambient air pollutants and spontaneous abortion. Further studies need to be done to examine possible correlations between personal exposure to air pollutants and pregnancy loss.