Breathing in Pollution While Pregnant Linked to Autism 3rd trimester seems to be the most at-risk time to inhale fine particulate matter By Jenn Gidman, Newser Staff Posted Dec 19, 2014 11:09 AM CST 80 comments Comments The particulates in the air could have a negative effect on the fetus, a new study says. (Shutterstock) (Newser) – It's probably not good for anyone to take a deep gulp of polluted air, but for pregnant women it could have a particularly significant effect—including maybe even upping the risk of having an autistic child, Bloomberg reports. A Harvard study published yesterday in Environmental Health Perspectives says that women exposed to high levels of air pollution during their third trimester had about double the risk of giving birth to a child with autism. The research makes use of a study of more than 116,000 American nurses that began in 1989, along with the EPA's air pollution data, NBC News reports. Of the 1,767 kids born to the nurses from 1990 to 2002, 245 of them were diagnosed with autism, Bloomberg notes. The causes of autism remain a mystery for the most part, with scientists debating the roles that both genes and environmental factors play. "There [have] to be gene and environmental interactions," the chairwoman of the Lerner Research Institute’s Genomic Medicine Institute (part of the Cleveland Clinic) tells Bloomberg. "I suspect the fetus already had the weak autism spectrum disorder genes, and then the genes and the environment interacted." This study isn't the first one to make the pollution/autism link, but it's "among the strongest studies to date," a director from advocacy group Autism Speaks tells NBC. Although it's hard to avoid pollution if you live near a big city or industrial factory—and fine particulates can drift hundreds of miles from their source, Bloomberg notes—the study's authors recommend pregnant women stay away as much as possible from cities beset by pollution and not exercise outside near traffic-heavy areas.