Environmental Exposures and Autism
Where birth defects increased, so did diagnoses of the developmental disorder, study showed
On the other hand, some studies have found a link between high exposure to air pollution during pregnancy and an increased autism risk, Halladay said.
Researchers continue to look for the environmental players in autism, Halladay said. Autism Speaks has a program that funds research on the environmental factors -- including toxic exposures and nutrition during pregnancy -- that might affect autism risk.
Rzhetsky said he hopes his team's findings help fuel the interest in that type of research. "There is a lot of research focused on the genetics," he said. "But environment plays a big role."
But chemicals in the environment are only one potential reason autism rates vary across the United States.
Rzhetsky's team also found lower rates of autism in states where regulations require a doctor's diagnosis of autism before kids can qualify for special education.
Halladay said the finding is consistent with past studies suggesting that differences in diagnosis help explain regional differences in autism rates.
A 2012 study from the U.S. Centers for Disease Control and Prevention found that one in 88 U.S. children had an autism spectrum disorder -- up almost 25 percent from just a few years before. But the rate varied widely, from one in 47 in Utah to one in 210 in Alabama.
Experts speculated that the national increase had a lot to do with better detection, and that differences in awareness and autism services might explain the regional differences.