Improved biomass stoves may not reduce indoor air pollution as much as is needed to have an impact on adverse birth outcomes.
Two trials in rural southern Nepal reduced indoor air pollution through improved biomass or liquid petroleum gas stoves, but levels were still much higher than World Health Organization standards.
Exposure of pregnant women to these lower air pollution levels was not associated with reduced incidence of low birth weight, preterm birth, and small for gestational age.
Few randomized trials have assessed the impact of reducing household air pollution from biomass stoves on adverse birth outcomes in low-income countries.
Two sequential trials were conducted in rural low-lying Nepal. Trial 1 was a cluster-randomized step-wedge trial comparing traditional biomass stoves and improved biomass stoves vented with a chimney. Trial 2 was a parallel household-randomized trial comparing vented biomass stoves and liquid petroleum gas (LPG) stoves with a year’s supply of gas. Kitchen particulate matter of 2.5 μm or less (PM 2.5) and carbon monoxide (CO) were assessed before and after stove installation. Prevalent and incident pregnancies were enrolled at baseline and throughout the trials. Birth anthropometry was compared across differing exposure times in pregnancy.
In trial 1, the mean 20-hour kitchen PM 2.5 concentration was reduced from 1380 µg/m 3 to 936 µg/m 3. Among infants born before the intervention, mean birth weight and gestational age were 2627 g (SD=443) and 38.8 weeks (SD=3.1), and 39% were low birth weight (LBW), 22% preterm, and 55% small for gestational age (SGA). Adverse birth outcomes were not significantly different with increasing exposure to improved stoves during pregnancy. In trial 2, the mean 20-hour PM 2.5 concentration was 885 µg/m 3 in households with vented biomass and 442 µg/m 3 in those with LPG stoves. Mean birth weight was 2780 g (SD=427) and 2742 g (SD=431), among households with vented and LPG stoves, respectively. Respective percentages for LBW, SGA, and preterm were 23%, 13%, and 42% in the vented stove group and not statistically different from 31%, 17%, and 42% in the LPG group.
Improved biomass or LPG stoves did not reduce adverse birth outcomes. PM 2.5 and CO following improved stove installation remained well above the World Health Organization indoor air standard of 25 µg/m 3 or intermediate air quality guideline of 37.5 µg/m 3. Trials that lower indoor air pollution further are needed.