Prenatal exposure to particulate matter (PM2.5) and low birth weight in a Sri Lankan birth cohort

Background: About 74% of the Sri Lankan population use biomass in the form of unprocessed wood as the primary cooking fuel. A growing body of evidence from meta-analyses and individual studies although limited by few prospective studies, report that prenatal exposure to particulate matter of size 2.5 μm (PM2.5) emissions from biomass fuel burning may be associated with low birth weight (LBW) (<2500 grams). We present results examining the association between PM2.5 and LBW in context of a birth cohort study in Sri Lanka. Methods: We followed 545 pregnant women from their first trimester until delivery and assessed outcomes at birth. Exposure to household air pollution (HAP) from biomass smoke was assessed using detailed questionnaire about fuel type, kitchen characteristics and cooking practices; two-hour measurements of kitchen PM2.5 were collected in a subset of households (n=304, 56%). Data from questionnaires and measured PM2.5 were used to estimate two-hour kitchen PM2.5 concentrations in unmeasured households. Data on covariates related to household characteristics, socio-demographic, maternal health and lifestyle factors were collected from baseline interviews. We performed linear and logistic regression analysis to evaluate the association between HAP exposure, and birth weight and LBW. Results: Of the total, 78% of the households used wood as primary or secondary fuel (n=425); households using wood had four-fold higher PM2.5 levels compared to those using LPG. In linear regression models, we found an inverse association between a 10-unit increase in PM2.5 and birth weight (β, -0.03; SE, 0.02; p, 0.06) adjusted for covariates. Similarly, categorical HAP exposure (>50% wood use) was significantly associated with birth weight as compared to LPG users (β, -0.13; SE, 0.06; p, 0.0331). In logistic regression models, a 10-unit increase in PM2.5 was associated with increased odds for LBW (OR, 1.26; 95%CI, 1.02-1.55; p, 0.0355), while the prevalence of LBW was highest among >50% wood users (OR, 2.82; 95%CI, 1.18-6.73; p, 0.0124), as compared to those using >50% LPG with wood and only LPG users. The association between HAP exposure and birth weight/LBW were consistent among term births (n=486). Conclusions: The finding of a significant association between prenatal PM2.5 exposure and LBW in a low-middle income country (LMIC) setting where competing risk factors are minimal fills a gap in the body of evidence linking HAP from biomass smoke to LBW. These results underscore the crucial need to implement prevention and reduction of HAP exposure in LMICs where the HAP burden is high. Key words: Household air pollution, Low birth weight, Sri Lanka, Birth cohort