Exposure to wildfire smoke during pregnancy, particularly during the second and third trimesters, was linked with a higher risk of autism diagnosis in children, according to a large new study.
Autism diagnoses in the United States have increased significantly in recent decades, intensifying public concern over factors that might contribute to its prevalence.
The new study, published in JAMA Pediatrics, included 893,212 mother-child pairs enrolled in Medicaid — the US/state healthcare program for lower-income Americans — with children born across the United States between 2007 and 2014.
The researchers analyzed estimates of weekly wildfire smoke concentrations for each mother's residential ZIP code, focusing on inhalable particles 2.5 micrometers or smaller in diameter.
Every 0.75-microgram-per-cubic-meter increase in the average concentration of wildfire-related fine particles during pregnancy was associated with a 30% higher risk of a child's autism diagnosis by age 8, the researchers found.
Fine-particle pollution from sources other than wildfires was associated with smaller increases in autism diagnosis risk, they also noted.
The study was observational and cannot prove whether or how wildfire smoke causes autism. Its focus on Medicaid enrollees may also limit how broadly the findings apply, given likely socioeconomic differences from the broader population.
Still, the researchers recommend that pregnant women be aware of wildfire events, limit their time outdoors during smoke episodes, check local air-quality reports and follow guidance for sensitive groups when pollution levels are elevated.
More toxic than normal air pollution, wildfire smoke can linger in the air for weeks and travel thousands of miles. Particles can penetrate deep into the lungs and contribute to inflammation throughout the body.
“Exposure may occur even when smoke is not visible,” study leader Stefania Papatheodorou of the Rutgers School of Public Health in New Jersey said in a statement.
She urges healthcare providers to incorporate discussions of environmental hazards into routine prenatal care.
“Sometimes clinicians are not even aware of these risks,” she said.
