A randomized controlled trial of prenatal air pollution exposure and the development of allergic sensitization in infancy

Background: Prenatal exposure to PM2.5 has been associated with the development of allergic sensitization in children. We conducted a single-blind, randomized controlled trial in Ulaanbaatar, Mongolia to test the effectiveness of HEPA filter air cleaner use during pregnancy on the risk of allergic symptoms in the first year of life. Methods: We enrolled 540 pregnant women at 10.3 weeks’ gestation, on average, and randomly assigned them to the intervention group (N = 217), which received one or two air cleaners (depending on home size) to use from enrollment until childbirth, or the control group (N = 187). We measured indoor PM2.5 concentrations over 7-days at ~11 weeks’ gestation and again at ~31 weeks’ gestation. We surveyed mothers about eczema, wheeze, respiratory infections and otitis media in the first year of life. The effectiveness of the intervention was analyzed using logistic regression in intention-to-treat analyses. Results: Baseline characteristics were similar between the two groups. PM2.5 concentrations were 29% lower, on average, in intervention homes than control homes (95% CI: 21-37%). The prevalence of outcomes ranged from 8.2% for wheeze to 54% for eczema. The intervention was significantly associated with a reduction in wheeze (OR: 0.47, 95% CI: 0.22 – 0.97). For eczema (OR: 1.12, 95% CI: 0.76 – 1.66), otitis media (OR: 1.07, 95% CI: 0.64 – 1.76) and chest infections (OR: 0.91, 95% CI: 0.58 – 1.43), the 95% confidence intervals indicated both potential harmful and beneficial effects of the intervention. Conclusion: The use of HEPA filter air cleaners during pregnancy reduced the odds of parent-reported wheeze in the first year of life.