Abstract
When discussing the association between birth weight and air pollution, previous studies mainly focus on the maternal trimester-specific exposures during pregnancy, whereas the possible associations between birth weight and weekly-specific exposures have been largely neglected. We conducted a nested 1:4 matched case-control study in Jinan, China to examine the weekly-specific associations during pregnancy between maternal fine particulate matter (aerodynamic diameter < 2.5 μm, PM2.5), nitrogen dioxide (NO2), and sulfur dioxide (SO2) exposure and birth weight, which is under a representative scenario of very high pollution levels. Ambient air monitoring data from thirteen monitoring stations and daily mean temperature data for Jinan during 2013–2016 were continuously collected. Birth data were obtained from the largest maternity and child care hospital of this city during 2014–2016. Individual exposures to PM2.5, NO2, and SO2 during pregnancy were estimated using an inverse distance weighting method. Birth weight for gender-, gestational age-, and parity-specific standard score (BWGAP z-score) was calculated as the outcome of interest. Distributed lag non-linear models (DLNMs) were applied to estimate weekly-specific relationship between maternal air pollutant exposures and birth weight. For an increase of per inter-quartile range in maternal PM2.5 exposure concentration during pregnancy, the BWGAP z-score decreased significantly during the 27th–33th gestational weeks with the strongest association in the 30th gestational weeks (standard deviation units decrease in BWGAP z-score: −0.049, 95% CI: −0.080 −0.017, in three-pollutant model). No significant association between maternal weekly NO2 or SO2 BWGAP z-score was observed. In conclusion, this study provides evidence that maternal PM2.5 exposure during the 27th–33th gestational weeks may reduce the birth weight in the context of very high pollution level of PM2.5.
Highlights
According to the World Health Organization (WHO), it was estimated that more than 20 million infants born with low birth weight globally and over 90% of these LBW infants were born in developing countries [1, 2]
We conducted a nested 1:4 matched case-control study in Jinan, China to examine the weekly-specific associations during pregnancy between maternal fine particulate matter, nitrogen dioxide (NO2), and sulfur dioxide (SO2) exposure and birth weight, which is under a representative scenario of very high pollution levels
An increasing number of studies have analyzed the associations between maternal air pollutant exposures and LBW, and trimester-specific associations were generally reported in these studies but the trimester with the greatest association differed among them, which was attributed to differences in study designs, data sources, geographic factors, and exposure assessment strategies [11, 13–26]
Summary
According to the World Health Organization (WHO), it was estimated that more than 20 million infants born with low birth weight (birth weight less than 2500 g, LBW) globally and over 90% of these LBW infants were born in developing countries [1, 2]. An increasing number of studies have analyzed the associations between maternal air pollutant exposures and LBW, and trimester-specific associations were generally reported in these studies but the trimester with the greatest association differed among them, which was attributed to differences in study designs, data sources, geographic factors, and exposure assessment strategies [11, 13–26]. Warren et al reported that maternal PM2.5 exposure could increase the risk of delivering an infant with LBW during the 20th–23th gestational weeks, and Symanski et al identified the 21th–24th gestational weeks as critical exposure windows for small for gestational age [27, 28]. More evidence is needed to detect out exact maternal susceptible exposure windows for maternal air pollutant exposures, because it has important significance in understanding the underlying mechanisms and prenatal care departments can optimize preventive and management strategies for pregnant women basing on these findings [30]
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