Portable HEPA filter air cleaner use during pregnancy and children’s autistic behaviors at four years of age: The UGAAR randomized controlled trial

Developmental exposure to airborne particulate matter (PM) may increase children’s risk of developing autism spectrum disorder. We quantified the impact of reducing PM exposure during pregnancy on the development of autistic traits in children. We also assessed associations between indoor fine PM (PM₂.₅) concentrations during pregnancy and autistic traits. In this parallel-group randomized controlled trial, we randomized 540 non-smoking pregnant women to receive HEPA filter air cleaners or to a control group, which did not receive air cleaners. We administered the Social Responsiveness Scale (SRS-2) to caregivers when children were a median of 48 months (range: 48 to 51 months). Our primary outcome was the SRS-2 total T-score. We imputed missing data using multiple imputation with chained equations and our primary analysis was by intention to treat. In secondary analyses, we estimated associations between full pregnancy and trimester-specific indoor PM₂.₅ concentrations and T-scores. We enrolled participants at a median of 11 weeks’ gestation. Our analysis included 478 children (233 control, 245 intervention). The intervention reduced average indoor PM₂.₅ concentrations by 29 % (95 % CI: 21, 37 %). The mean SRS-2 total T-score was 0.5 units lower (95 % CI: −2.5, 1.5) among intervention participants, with evidence of larger benefits for children at the high end of the T-score distribution. An interquartile range (9.6 µg/m³) increase in indoor PM₂.₅ during pregnancy was associated with 1.8-unit (95 % CI: 0.3, 3.2) increase in mean SRS-2 total T-score. Effect estimates for PM₂.₅ concentrations by trimester were smaller and confidence intervals spanned no effect. Reducing indoor PM during pregnancy had little impact on mean autism-related behavior scores in children. However, indoor PM₂.₅ concentrations during pregnancy were associated with higher scores. Exposure to particulate matter during pregnancy may influence the development of autistic traits in childhood. Trial registration: ClinicalTrials.gov: NCT01741051.