- Design
- Population-based cohort using US Medicaid claims
- Population
- 893,212 mother-child pairs
- Primary outcome
- Incident autism and ADHD diagnoses
- Effect
- Autism HR 1.30 (1.07–1.59); ADHD HR 1.03 (0.91–1.17) per 0.75 µg/m³
A US cohort of 893,212 mother-child pairs in Medicaid estimated weekly wildfire-attributable fine particulate (PM2.5) exposure at each mother's postcode during pregnancy and followed the children for diagnoses of autism and ADHD.
By age 8, cumulative incidence was 1.9% for autism and 10.4% for ADHD. Each interquartile increase in wildfire PM2.5 over pregnancy (0.75 µg/m³) was associated with a higher risk of autism (HR 1.30, 95% CI 1.07–1.59), with the strongest association in mid to late gestation. There was no association with ADHD (HR 1.03, 0.91–1.17).
This is observational and exposure is estimated by area, not measured in each woman. It adds to evidence that particulate exposure in pregnancy may affect neurodevelopment. In India the dominant sources are crop burning, traffic and household fuel rather than wildfires, so the specific estimate does not transfer, but the general advice to limit exposure in pregnancy does.
- Advise pregnant women to limit outdoor exposure on high-pollution days where practical.
- Ask about household solid fuel use in pregnancy and discuss cleaner alternatives.
- Do not attribute an individual child's autism to air pollution on this evidence.
- Keep developmental surveillance unchanged; this finding does not alter screening.
Why it matters
Air quality in pregnancy is becoming a neurodevelopmental question, not only a respiratory one.
Don't overread it
This is an association based on area-level exposure; it cannot show that smoke causes autism.
The statistics, in plain English
An HR of 1.30 means about 30% higher risk per step of exposure, but from a low base of under 2%. The ADHD interval crosses 1.0, so no association was shown there.
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