LOS ANGELES, Jan. 22 (Xinhua) -- A newly published study reported an association between prenatal exposure to wildfire smoke in Southern California and a higher likelihood of autism diagnosis in early childhood.

According to a study published online Tuesday in the journal Environmental Science and Technology, researchers examined a large pregnancy cohort in Southern California and estimated mothers' exposure to wildfire smoke and wildfire-related fine particulate matter known as PM2.5 at their residential addresses during their pregnancies from 2006 to 2014. The researchers then linked those exposure estimates to autism diagnoses by age 5, using time-to-event statistical modeling.

The study reported that the association was most consistent in the third trimester and appeared clearer when exposure was measured by the number of days or waves of wildfire smoke, rather than by the average concentration of wildfire PM2.5 alone.

In a sensitivity analysis focusing on mothers who did not change address during pregnancy, the study reported that third-trimester exposure to more than 10 wildfire smoke days, compared with none, was associated with a hazard ratio of 1.225. The study also reported smaller increases for fewer smoke days.

The findings are relevant to the Los Angeles region because wildfire smoke can travel long distances and affect downwind communities, including the Los Angeles basin, even when fires burn outside city limits.

These findings align with broader research on air pollution and autism risk. A 2021 meta-analysis from Harvard T.H. Chan School of Public Health reported higher autism risk associated with PM2.5 exposure, with prenatal risk appearing strongest in the third trimester.

Meanwhile, researchers cautioned that while observational studies can identify correlations, they cannot prove that wildfire smoke causes autism. Estimates of exposure based on home addresses cannot fully capture individual behaviors, such as time spent indoors or use of air filtration, and other factors may contribute to the observed patterns. ■