Ulaanbaatar (Mongolia) is one of the most air polluted capital cities in the world, with ambient
sulfide dioxide (SO2) and particulate matter PM10 and PM2.5 levels > 23 times World Health Organization
(WHO) standards in winter. Several studies have examined the effects of air pollution on
pregnancy, providing that exposure to ambient air pollutants is associated with poor birth outcome,
such as low birth weight. Our study goal was to study the associations between air pollution
exposures during pregnancy and low birth weight among all full-term births (gestational age 37 -
42 weeks) for a 6-year period (January 2008 through December 31, 2013) in Ulaanbaatar, Mongolia.
In the study we recruited 160,676 singletons. We used a logistic regression adjusting for gestational
age, parental education level, parity and infant age. The adjusted relative risk of low birth
weight was 1.06 (95% CI = 1.01 - 1.12) for each inter-quartile increase in NO2 concentrations. The
risk of low birth weight was increased to 1.04 (95% CI = 0.93 - 1.15) for CO, 1.02 (95% CI 0.97 -
1.05) for SO2 and 1.03 (95% CI 1.01 - 1.08) for PM10. Each inter-quartile increase of NO2 concentration
during the first trimester reduced 10.74 gm of birth weight. SO2, CO and PM10 also decreased
birth weight 7.62, 7.49, and 8.72 gm, respectively. Each inter-quartile increase of pollutants decreases
baby weight up to 11 grams.