A randomized controlled trial of air cleaner use during pregnancy and wheeze in early childhood

Background: Air pollution is a major threat to public health. I investigated the impact of HEPA filter air cleaners use during pregnancy on wheezing in childhood using data from the Ulaanbaatar Gestation and Air Pollution Research (UGAAR) randomized controlled trial. Methods: Study staff randomly assigned 540 pregnant women to an intervention group that received HEPA cleaners during pregnancy or a control group that received no air cleaners (N = 268 intervention and 272 control). During the children's first four years of life, staff administered a questionnaire to caregivers at six-month intervals to assess wheezing in children. I identified the presence or absence of wheezing in each year and categorized children into four wheeze phenotypes: ever wheezers, persistent wheezers, late-onset wheezers, or early-transient wheezers. I also quantified the number of wheezing episodes in the first and second years of life and the third and fourth years of life. The primary analysis was intention to treat. In a secondary analysis, I estimated the relationship between modelled indoor PM2.5 concentrations, averaged over pregnancy and each trimester, and wheeze outcomes. Results: My analysis included 481 children (236 intervention, 245 control) born at a median gestational age of 39.5 weeks. The intervention reduced average indoor PM2.5 by 29% (95% CI: 21, 37%). Over half (54%) of the children experienced a wheezing episode before age four. The intervention was not associated with the frequency of wheeze or with any wheezing phenotypes. In my secondary analysis, an interquartile range increase in indoor PM2.5 during the first trimester was associated with increased odds of late-onset wheeze (OR: 1.84, 95% CI: 1.13, 3.01). There were no associations between PM2.5 concentrations and other phenotypes. Conclusion: The HEPA air cleaner intervention during pregnancy did not reduce the frequency of wheeze episodes or the odds of wheeze phenotypes. Future research is needed to investigate the impact of air pollution interventions on late-onset wheeze.