Air pollution - especially PAHs from Traffic - associated with up to 30 percent increase in risk of premature birth

University of California, looked at 100,000 births occuring within 5 miles of air quality monitoring stations.

Traffic-related air pollution, especially polycyclic aromatic hydrocarbons (PAH), is associated with up to a 30% increase in premature births, and that seasonal changes and vicinity to the coast affected concentration of toxic pollutants in the air.

Some pollutants were area specific, relating to industry and urbanization. However, overall exposure to critical pollutants such as PAH resulted in up to a 30% increase in the risk of premature birth.

Other toxic substances, such as benzene and fine particulate matter from diesel fumes were associated with a 10% increase,

Ammonium nitrate fine particles were associated with a 21% increase in premature birth.

Concentrations of these pollutants were higher in winter and lower in coastal areas, indicating that local weather patterns played an important part in the dispersal of pollutants.

http://www.sciencecodex.com/read/pregnant_mothers_at_risk_from_air_pollution-79407