Exposure to wildfire smoke late in pregnancy may raise child autism risk

Exposure to wildfire smoke in late pregnancy may raise the chance a child is later diagnosed with autism, a recent study has found.

The study analysed more than 200,000 births in Southern California from 2006 to 2014.

Researchers found that children whose mothers were exposed to smoke during the third trimester were more likely to be diagnosed with autism by age five.

The strongest association was seen among mothers exposed to more than 10 days of smoke during the final three months of pregnancy.

In that group, children had a 23 per cent higher risk of diagnosis compared with those whose mothers were never exposed during pregnancy.

The study, led by Tulane University researchers, is the first to examine the potential link between prenatal wildfire smoke exposure and autism.

The findings do not prove a causal link but add to evidence that air pollutants can harm foetal neurological development.

Mostafijur Rahman is corresponding author and assistant professor of environmental health sciences at the Celia Scott Weatherhead School of Public Health and Tropical Medicine at Tulane University.

The researcher said: “Both autism and wildfires are on the rise, and this study is just the beginning of investigating links between the two.

“As climate change increases the frequency and intensity of wildfires in many parts of the world, understanding their relationship with autism is important to being able to develop preventive policy and interventions that will protect pregnant women and their children.

The study focused solely on California, which leads the nation in both yearly acres burned by wildfire and rates of childhood autism diagnoses.

It also comes one year after the Eaton and Palisades fires destroyed more than 16,000 structures in the second and third most destructive California wildfires on record, respectively.

Since 2000, the prevalence of Autism diagnoses has increased each year, a trend often attributed in part to greater awareness and screening.

Research has also linked prenatal exposure to air pollution with risk, with heavy metals in particles a commonly theorised culprit.

Fires can cause high spikes of air pollution in a short time. Burning vegetation and buildings release toxic metals and other pollutants that can be inhaled.

Fine particles in smoke can pose a threat regardless of toxicity. Inhalation of smoke can cause inflammation and stress.

In the study, mothers of children diagnosed with autism tended to be older, more likely never to have had a previous pregnancy, and had a higher prevalence of pre-pregnancy diabetes and obesity.

Four times as many boys were diagnosed with autism as girls.

The potential association in the third trimester aligns with a 2021 Harvard University study that also found a higher risk in children linked to air pollution exposure during late pregnancy, a period marked by rapid foetal brain growth and development.

David Luglio is lead author and post-doctoral fellow with the Celia Scott Weatherhead School of Public Health and Tropical Medicine.

He said: “Further study is needed to understand how wildfire smoke exposure to pregnant mothers could cause autism in their children, and to determine how exposure may interact with biology, genetics and other environmental exposures.

“This study is just one piece of a much larger puzzle, and the findings tell us there are more pieces to be put together.”