Are there differences in birth weight according to sex and associations with maternal exposure to air pollutants? A cohort study

ABSTRACT CONTEXT AND OBJECTIVE: Several effects of exposure to air pollutants on human health are known. The aim of this study was to identify whether exposure of pregnant women to air pollutants contributes towards low birth weight and which sex is more affected. DESIGN AND SETTING: Longitudinal study using data on newborns from mothers living in São José do Rio Preto (SP) who were exposed to air pollutants in 2012-2013. METHODS: A hierarchical model on three levels was built using maternal and newborn variables and environmental concentrations of particulate matter, ozone and nitrogen dioxide in quartiles. Preterm new-borns, twins and newborns with birth defects were excluded and exposure windows of 30, 60 and 90 days before delivery were considered. RESULTS: 8,948 newborns were included: 4,491 males (50.2%) and 4,457 females (49.8%); 301 newborns presented low birth weight (3.4%). The mean weight differed between males (3281.0 g) and females (3146.4 g) (P < 0.001). Exposure to ozone was significantly associated with low birth weight in both sexes in the 30-day window (odds ratio, OR = 1.38) and 90-day window (OR = 1.48); and among females, in the 30-day window (OR = 1.58) and 90-day window (OR = 1.59). Exposure to particulate matter had a paradoxical protective effect. No association was found among male newborns. CONCLUSIONS: Female newborns showed greater susceptibility to maternal exposure to air pollutants. Studies on low birth weight in relation to maternal exposure to air pollutants should deal with males and females separately.

摘要背景与研究目标：目前学界已明确大气污染物暴露对人体健康的多种影响。本研究旨在探究妊娠期女性暴露于大气污染物是否会增加低出生体重儿的发生风险，以及何种性别的新生儿更易受此影响。
研究设计与研究场景：本研究为纵向研究，使用2012-2013年居住于巴西圣保罗州圣若泽杜里约普雷托市、存在大气污染物暴露的妊娠女性的新生儿相关数据。
研究方法：本研究构建了三级分层模型，纳入母亲与新生儿相关变量，以及按四分位数分组的颗粒物、臭氧与二氧化氮环境浓度数据。本研究排除了早产儿、双胎及存在出生缺陷的新生儿，并考量了分娩前30、60、90天的暴露窗口期。
研究结果：本研究共纳入8948名新生儿，其中男性4491名（50.2%），女性4457名（49.8%）；301名新生儿为低出生体重儿（占比3.4%）。男性新生儿平均出生体重为3281.0g，女性为3146.4g，组间差异具有统计学意义（P < 0.001）。在分娩前30天与90天的暴露窗期中，臭氧暴露与两种性别的低出生体重发生风险均呈显著正相关（比值比（Odds Ratio，OR）=1.38与OR=1.48）；其中女性新生儿在上述两个窗期中的关联更为显著（OR=1.58与OR=1.59）。颗粒物暴露则呈现出反常的保护效应，且未在男性新生儿中观察到此类关联。
研究结论：女性新生儿相较于男性，对母体大气污染物暴露的易感性更高。针对母体大气污染物暴露与低出生体重关联的相关研究，应分别对男性与女性新生儿进行分析。