NEW ORLEANS — Exposure to wildfire smoke during the final three months of pregnancy is linked to a higher risk of autism in children, according to a study released Tuesday by researchers at Tulane University.

The research, published in the journal Environmental Science & Technology, analyzed health records and air quality data for more than 200,000 births in Southern California between 2006 and 2014. The study aimed to understand how tiny smoke particles affect a baby’s development before birth.

Specific Risks Identified

According to the findings, the risk of an autism diagnosis was about 10% higher for children whose mothers were exposed to smoke for one to five days during the third trimester. The risk rose to 23% for children whose mothers were exposed for more than 10 days.

Researchers focused on tiny air pollution particles known as PM 2.5—microscopic bits of dust and soot that are about 30 times smaller than the width of a human hair. These particles are small enough to be inhaled deep into a mother’s lungs and enter her bloodstream. According to the researchers, the last three months of pregnancy are a critical time for a baby’s brain, as it grows rapidly and different regions begin to form.

These results are especially significant for California. The state leads the nation in both the amount of land burned by wildfires and the rate of autism diagnoses. According to the Centers for Disease Control and Prevention (CDC), about 1 in 31 school-age children nationwide currently have autism.

Expert Caution

While the study shows a link, some experts say it is too early to draw firm conclusions. David Mandell, a psychiatry professor not involved in the study, noted that the link between smoke and autism risk did not appear in every group of people studied.

Mandell also expressed doubt because the risk levels did not always rise steadily as smoke exposure increased, suggesting the data was inconsistent based on the length of exposure. He said he wants to see other researchers repeat the study before fully trusting the results.

The research also had limitations because it used general estimates for outdoor air quality instead of measuring the air quality inside the mothers’ homes. Researchers also did not know if the mothers used air purifiers or wore masks on smoky days.

National Research Priorities

On a broader scale, the federal government is focusing more on how the environment affects health. U.S. Health Secretary Robert F. Kennedy Jr. has prioritized new studies on how environmental factors, including air pollution and chemicals, might contribute to autism.

Health officials are looking at wildfire smoke as part of a larger effort to answer parents' questions about pregnancy safety. This effort includes investigating new environmental triggers while also clearing up old misconceptions. As part of this effort to clear up misconceptions, the World Health Organization also recently noted that there is no proven link between autism and Tylenol use during pregnancy. By sharing these facts, medical organizations hope to give parents clearer information about their baby’s health and safety.