Mothers with higher exposure to DDT, a blacklisted chemical once widely used in North America, are at significantly greater risk to give birth to a child with autism, a new study suggests.

The research, published Thursday in the American Journal of Psychiatry, raises new concerns about the pervasive substance, which was banned in Canada 30 years ago but is almost impossible to eliminate from the environment.

Using data from Finland, researchers compared blood samples from 778 mothers of children with autism against a group of 778 mothers of children without autism. They tested blood samples for DDE, a byproduct of DDT exposure that appears in the bloodstream.

The team found that mothers with higher DDE levels had a 32-per-cent higher chance of giving birth to a child with autism.

The study is not proof that DDT exposure directly causes autism, and the authors say more research is necessary to replicate their findings.

Regardless, the report offers “another piece of the puzzle” to help scientists determine what factors cause autism, said lead author Dr. Alan Brown.

“If a pregnant mother is exposed to this chemical, her unborn baby’s brain might develop differently and in such a way that it might increase the risk of maybe later getting autism,” Dr. Brown told CTV News.

DDT, formally known as dichlorodiphenyltrichloroethane, was banned in dozens of countries across the world, including Canada, after concerns first arose in the 1970s about the chemical’s impact on human mental and physical health. DDT is still used in some developing countries as a means of pest control.

Dozens of genes are involved in the development of autism spectrum disorder. Dr. Evdokia Anagnostou, a child neurologist and senior clinician scientist at Holland Bloorview Kids Rehabilitation Hospital, said research like this helps provide a clearer picture of the condition.

“It’s important to think about the mechanisms by which genes and environmental toxicants interact to produce harm in brain development so that we can make better decisions as we move along,” Dr. Anagnostou said.

Susan Cosgrove has two children with autism spectrum disorder. She says it’s natural for parents to want to know why their kids develop the condition, but she cautioned against living “in fear of things that we cannot control.”

With all the challenges of being a parent of a child with autism, it’s important that parents focus on the things they can control, Cosgrove said.

“Remember to keep yourself as healthy as you can and your little one as healthy as you can,” she said.

With a report from CTV Medical Correspondent Avis Favaro and senior producer Elizabeth St. Philip