A randomized air cleaner intervention study of social and behavioral impairment in childhood: The Ulaanbaatar Gestation and Air Pollution Research (UGAAR) study

Background: Maternal exposure to particulate matter (PM) air pollution during pregnancy may impair children's social and behavioral development. My objectives were to assess (1) the impact of reducing indoor PM using portable HEPA cleaners during pregnancy on behavioral problems at ages 2 and 4 (2) the impact of reducing indoor PM using portable HEPA cleaners during pregnancy on the autistic traits at age 4 and, (3) the influence of prenatal maternal stress on the relationship between the intervention and children's social and behavioral outcomes at age 4. Methods: This research used data collected in the Ulaanbaatar Gestation and Air Pollution Research (UGAAR) randomized controlled trial. A total of 540 non-smoking pregnant women were randomly assigned to receive 1 to 2 HEPA filter air cleaners or no air cleaners. The HEPA air cleaners were deployed at median of 11 weeks of pregnancy. UGAAR staff collected exposure data through home visits and health, demographic data, and hair and blood samples through clinic visits during pregnancy. Staff also administered the Behavior Assessment System for Children, 3rd Edition (BASC-3) when children were two and four years old and the Social Responsiveness Scale, Second Edition (SRS-2) at four years old. Blood samples were also collected from children at age two. I imputed missing data using multiple imputation with chained equations and assessed the effect of the intervention on mean BASC-3 and SRS-2 scores. I also evaluated adjusted associations between trimester-specific PM2.5 concentrations inside residences and behaviour scores. Finally, I tested modification of the intervention's effect on behaviour by maternal stress hormone concentrations and perceived stress in early pregnancy. Results: No differences in the mean BASC-3 and SRS-2 scores between treatment groups were observed. An interquartile range (20.1 µg/m3) increase in first trimester PM2.5 concentration was associated with higher externalizing problem scores (2.4 units, 95% CI: 0.7, 4.1), higher internalizing problem scores (2.4 units, 95% CI: 0.7, 4.0), lower adaptive skills scores (-1.5 units, 95% CI: -3.0, 0.0), and higher behavior symptoms index scores (2.3 units, 95% CI: 0.7, 3.9) when children were 4 years old. I found evidence of interactions between the intervention and maternal stress, with generally greater benefits of the intervention on behavior scores among children whose mothers had higher levels of stress in early pregnancy. Conclusion: This work provides further evidence that PM2.5 exposure during pregnancy increases the risk of social and behavioral problems in children. It may be necessary to intervene early in pregnancy to protect children.