A study of three million infants across nine nations, including the U.S., South Korea and Brazil, finds a connection between inhaled particulate matter and low birth weight in infants

http://www.scientificamerican.com/article.cfm?id=air-pollution-delivers-smaller-babies

The original article: http://ehp.niehs.nih.gov/2013/02/1205575

See these sources too:

 http://www.nature.com/news/air-pollution-delivers-smaller-babies-1.12358


http://www.ucsf.edu/news/2013/02/13487/maternal-exposure-air-pollution-linked-low-birth-weights-worldwide

http://www.medpagetoday.com/PublicHealthPolicy/EnvironmentalHealth/37279