Maternal Secondhand Smoke Exposure Enhances Macrosomia Risk among Pregnant Women Exposed to PM2.5: A New Interaction of Two Air Pollutants in A Nationwide Cohort

Abstract BACKGROUND Previous studies have been controversial and inconsistent about fine particulate matter (PM2.5) and secondhand smoking (SHS) air pollutants on neonatal birthweight outcomes and there were no published studies assessing the potential interactive effects between PM2.5 and SHS on birthweight outcomes. PURPOSE To investigate interaction between gestational PM2.5 and SHS air pollution exposure on the risk of macrosomia among pregnant women. METHODS Research data were derived from National Free Preconception Health Examination Project (NFPHEP). Data cleaning process was conducted following strict screening standards to ensure eligibility of participants in our study. Different interaction models about air pollution on birthweight outcomes were established, according to different confounding factors adjustment and different pregnancy stages. SHS subgroups analysis were conducted to further confirm the results of interaction models. RESULTS Totally, 197877 participants were included in our study. In full-adjusted interaction model, maternal exposure to PM2.5 was associated with an increased risk of macrosomia in whole (p < 0.001), the first (p < 0.001), second (p < 0.001) and third (p < 0.001) trimester of pregnancy. However, there was a trend for gestational exposure to SHS with risk of low birthweight, but not statistically significant (occasional SHS exposure (p = 0.099); frequent SHS exposure (p = 0.272)). Interaction effect was statistically significant between maternal exposure to PM2.5 and SHS on the risk of macrosomia in the whole pregnancy (all interaction p < 0.050) and the first trimester pregnancy (all interaction p < 0.050), not in the second (all interaction p > 0.050) or third trimester (all interaction p > 0.050) of pregnancy. The higher frequency of SHS exposure prompts stronger interaction between the two air pollutants in the whole and the first trimester pregnancy. CONCLUSIONS In the whole pregnancy and the first trimester pregnancy, maternal exposure to SHS during pregnancy enhances the risk of macrosomia among pregnant women exposed to PM2.5 air pollutant, and the interaction became stronger with more frequent exposure to SHS.