Objective To investigate the exposure-response relationship between prenatal exposure to mixed air pollutants and placental and fetal development.

Methods Based on the information on pregnant women and their placentas and newborns from a prospective birth cohort study conducted in Guangzhou, China from 2016 to 2017. Quantile g-computation was applied to assess the combined effects of prenatal exposure to mixed air pollutants on placental development indicators (placental weight, placental volume, and placental weight ratiothe ratio of placental weight to neonatal weight at birth) and neonatal birth weight, and explore the sensitive windows and vulnerable populations for prenatal exposure.

Results The values of mean±standard deviation of placental weight, placental volume, placental weight ratio, and neonatal birth weight for all participants were (524.10±66.50)g, (730.10±186.40)cm³, 16.94%±3.40%, and (3 154.07±448.41)g, respectively. Early prenatal exposure to mixed air pollutants was negatively associated with placental weight (β=-5.34 g, 95% confidence intervalCI: -9.64 g to -1.04 g) and placental volume (β=-13.16 cm³, 95%CI: -24.73 cm³ to -1.60 cm³), but late prenatal exposure to the mixture was positively associated with placental weight (β=7.76 g, 95%CI: 1.78 g to 13.73 g) and placental weight ratio (β=0.50%, 95%CI: 0.20% to 0.80%). According to the stratified analyses, for pregnant women who conceived in the cold season, there were stronger associations of pollutant mixture exposure with placental weight ratio (β=0.55%, 95%CI: 0.31% to 0.79%) and neonatal birth weight (β=-54.87 g, 95%CI: -91.02 g to -18.72 g); for those who conceived during the warm season, pollutant mixture exposure also decreased placental weight (β=-4.80 g, 95%CI: -9.11 g to -0.50 g) and placental weight ratio (β=-0.26%, 95%CI: -0.49% to -0.03%). For pregnant women who gained inadequate weight during pregnancy, placental weight ratio (β=0.53%, 95%CI: 0.02% to 1.05%) and neonatal birth weight (β=-98.94 g, 95%CI: -172.79 g to -25.09 g) were more susceptible to pollutant mixture exposure.

Conclusion Mixed air pollutant exposure in early pregnancy is negatively associated with placental weight and placental volume, and pollutant exposure in late pregnancy is positively associated with placental weight and placental weight ratio. Air pollutant exposure produces varying degrees of effects on the placenta and fetus of pregnant women conceiving in different seasons or gaining insufficient weight during pregnancy.