Exposure to high levels of air pollutants during the coldest months of the year in Ulaanbaatar, Mongolia, is associated with a high incidence of spontaneous abortion during those months, according to a report by researchers from Mongolia and the United States (Enkhmaa D et al. BMC Pregnancy Childbirth. doi:10.1186/1471-2393-14-146 [published online April 23, 2014]).
The coldest capital city in the world (and one of the most polluted), Ulaanbaatar experiences great fluctuations in air pollution throughout the year. The use of coal-burning stoves to heat homes causes high levels of air pollutants during winter, in contrast to much better air quality in summer. Air pollution has been strongly associated with adverse effects on reproductive health, and several recent studies have reported an increase in fetal loss early in pregnancy with exposure to high levels of air pollutants.
Friedrich MJ. Spontaneous Abortions in Mongolia Linked to High Air Pollutant Levels. JAMA. 2014;311(23):2372. doi:10.1001/jama.2014.6622