NEW ORLEANS — Women breathing wildfire smoke late in pregnancy had a higher risk of having a child later diagnosed with autism, even when the smoke exposure lasted only a few days, according to a study by Tulane University researchers.
The study, published in Environmental Science & Technology recently, followed over 204,000 mother-child pairs in Southern California from 2006 to 2014, using medical records and estimated fine particulate matter at the mothers’ home addresses.
Women who were exposed to wildfire smoke for more than 10 days in the third trimester — weeks 28 to 40 — had about a 23% higher risk of having a child later diagnosed with autism compared with women who had no smoke exposure during that period. But even shorter exposures mattered.
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“Even a one-day or two-day exposure is still 10%,” said Mostafijur Rahman, an assistant professor of environmental health sciences at Tulane University’s Celia Scott Weatherhead School of Public Health and Tropical Medicine and a co-author of the study. “Ten percent is also a big number.”
In terms of hard numbers, the risk is still small for individual pregnancies.
Air pollution and developing babies
Wildfires produce tiny, inhalable particles called PM2.5 that are about 30 times smaller than the diameter of a single strand of hair. They are a toxic concoction made up of particles from burned vegetation, soot from incomplete combustion, chemical salts formed in smoke, trace metals released as materials burn, and additional particles that form in the air as gases from fire react with other pollutants.
Louisiana does not typically have the same amount of smoke exposure as Southern California. But the state does have wildfires and other sources of air pollution. In 2023, smoke from peat fires — smoldering layers of marsh — blanketed the New Orleans area for weeks and wildfires in western Louisiana burned 60,000 acres. In 2025, a fire at Smitty’s Supply, an industrial facility in Roseland, sent smoke and black soot raining down into nearby neighborhoods. And the heavily industrialized corridor known as “Cancer Alley” between Baton Rouge and New Orleans has long faced persistent pollution from petrochemical plants, refineries and manufacturing facilities.
“We do know that air pollution — whatever form it is — is not good,” said study author David Luglio.
The research team has previously found that air pollution in general is associated with an increase in autism.
“Air pollution itself is bad, whether it is coming from wildfire, petrochemical industry or traffic,” said Rahman.
Why the 3rd trimester?
While most major organs are formed earlier in pregnancy, the third trimester is a period when the brain and lungs are developing rapidly and are vulnerable to even modest disruptions in oxygen delivery.
“Air pollution can increase inflammation and oxidative stress in the mother, potentially affecting placental function and blood flow,” said Dr. Stefania Papatheodorou, an OB-GYN and environmental epidemiologist at Rutgers University.
Papatheodorou said the findings are relevant for regions like Louisiana, even if there is not the same amount of wildfire smoke.
“Although the sources and composition differ, many of the harmful components overlap,” she said. “Both wildfire smoke and industrial pollution contain fine particulate matter and other toxic gases that can be inhaled and enter the bloodstream.”
At the same time, she tries to reassure patients that most pregnancies result in healthy babies, even in areas with air pollution. Pregnant people should pay attention to air-quality alerts and limit outdoor activity on poor-quality days, using air conditioning and keeping windows closed. A well-fitted N-95 mask is also effective at filtering out PM 2.5.
“This is about risk reduction,” Papatheodorou said. “Pregnant people shouldn’t feel guilty or overly anxious, just informed and supported.”
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