A randomized air filter intervention study of air pollution and fetal growth in a highly polluted community: the Ulaanbaatar Gestation and Air Pollution Research (UGAAR) study

Background: Gestational exposure to fine particulate matter (PM2.5) and cadmium may impair fetal growth. Portable high efficiency particulate air (HEPA) filter air cleaners can reduce indoor PM2.5, but their effect on fetal growth has not been evaluated. Objectives: We assessed (1) HEPA cleaner effectiveness in reducing residential indoor PM2.5 and maternal blood cadmium, (2) the effect of HEPA cleaners on fetal growth, and (3) the relationship between maternal cadmium exposure and fetal growth, among non-smoking pregnant women in Ulaanbaatar, Mongolia. Methods: We randomized 540 participants at ≤ 18 weeks gestation to an intervention (1-2 HEPA cleaners in homes from early pregnancy until childbirth) or control (no HEPA cleaners) group. We collected exposure, health, and demographic data through home and clinic visits and from clinic records. We measured one-week indoor PM2.5 concentrations in early (~11 weeks gestation) and late (~31 weeks gestation) pregnancy, collected blood samples in late pregnancy for analysis of cadmium, and obtained birth data at delivery. We evaluated the effect of the intervention on our primary outcome, birth weight, and other fetal growth indicators using unadjusted linear and logistic regression and time-to-event analysis, in intention-to-treat analyses. We also used multiple linear and logistic regression to assess the relationships between log2-transformed blood cadmium and fetal growth. Results: HEPA cleaners reduced indoor PM2.5 and blood cadmium concentrations by 29% (95% CI: 21, 37%) and 14% (95% CI: 4, 23%), respectively. Among 463 live births, the median (25th, 75th percentile) birth weights for control and intervention participants were 3450 g (3150, 3800 g) and 3550 g (3200, 3800 g), respectively, but the intervention was not associated with an increase in birth weight (18 g; 95% CI: -84, 120 g). In a pre-specified subgroup analysis of 429 term births the intervention was associated with an 85 g (95% CI: 3, 167 g) increase in mean birth weight. A doubling of blood cadmium was associated with an 86 g (95% CI: 26, 145 g) reduction in birth weight. Conclusions: Our findings provide further evidence that PM2.5 and cadmium exposures during pregnancy impair fetal growth and that exposure reduction during pregnancy can reduce these effects. Portable HEPA cleaners are an effective household-level intervention but reductions in air pollution emissions are needed to realize the largest public health benefits.