Exposure to ambient particulate matter during pregnancy: Associations with birth weight in Thailand

Abstract

Background/Aim: Studies show birth weight (BW) is adversely associated with exposure to ambient particulate matter (PM) during pregnancy. Most research originates from high-income countries. The objective of this study was to quantify associations between BW and exposure to PM during pregnancy in Thailand.Methods: We obtained available hourly ambient air pollutant data (PM10, Ozone [O3], and Nitrogen Dioxide [NO2]) from the government-operated network of ground monitors and individual birth weight data in Thailand during 2015-2018. We performed an ecological analysis to evaluate the association between mean trimester (T) exposure to PM10 with BW and low BW (<2,500 g), adjusting for gestation age, sex, number of previous pregnancies, mother’s age, heat index, season, year, and NO2 and O3. We examined potential effect modification of PM10 exposure by sex and province.Results: There were 83,931 eligible births during the study period with a mean pregnancy PM10 exposure of 39.7 µg/m3 (SD = 7.7). In the continuous BW analysis, the entire pregnancy exposure to PM10 was associated with reduced BW only after adjustment for NO2 (-6.76 g [95% CI = -12.49 to -1.04] per 10 μg/m3 increment. In contrast with these findings, a reduced adjusted Odds Ratio (aOR) of LBW was associated with PM10 exposure in T1 (aOR = 0.953 [95% CI = 0.917 to 0.990]) and T2 (aOR = 0.942 [95% CI = 0.905 to 0.981]). Although some associations reached statistical significance, there was no consistent interaction observed by sex or province.Conclusions: We found weak evidence that average PM10 levels during the whole pregnancy were associated with small reductions in BW, but also found exposure in T1 and T2 had a lowered risk of LBW. These findings call for additional research of air pollution and BW in low and middle income countries with improved exposure estimates.