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Long-term exposure to air pollution and risk of preterm birth and low birth weight in Tehran, Iran

Introduction: Adverse effects of air pollution on human health has been identified as a major concern worldwide. We conducted this study to investigate the association between prenatal exposure to ambient air pollution and Low Birth Weight (LBW) and preterm among newborns in the megacity of Tehran. 
Materials and methods: This cross-sectional study was carried out on 1605 newborns. Data on the residential locations of mothers were collected from birth certificates. To estimate the prenatal exposure to air pollutants, data of 21 air quality monitoring stations in Tehran were used. The Man-Whitney test was used to estimate the association between exposure to ambient air pollution and LBW and preterm. 
Results: The mean birth weight in our analyses was 3117 g. A significant association was found between maternal exposure to particulate matter less than 2.5 µm (PM2.5) in the first trimester and incidence of preterm (p=0.011) and LBW (p=0.003) in newborns. Also, a close association was observed between exposure to Carbon Monoxide (CO) in the first and second trimesters and LBW (p=0.002, p=0.015). There were no statistically significant associations in LBW in the case of Particulate Matter less than 10 µm (PM10), Sulfur Dioxide (SO2), and Ozone (O3). 
Conclusion: The results revealed that the higher risk for LBW was related to ambient PM2.5 and CO. Since many factors may affect LBW, and the pathogenic mechanisms of the effect of air pollution on LBW have not been completely elucidated, the findings should be interpreted with caution and further studies need to be conducted on this issue considering the large sample size.