Prenatal Exposure of PFAS in Cohorts of Pregnant Women: Identifying the Critical Windows of Vulnerability and Health Implications.

Cohorts of pregnant women in 2018 and 2020 were selected to explore prenatal exposure to perfluoroalkyl and polyfluoroalkyl substances (PFAS). Maternal serum during the whole pregnancy (first to third trimesters) and matched cord serum were collected for the analysis of 50 PFAS. Perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and 6:2 fluorotelomer sulfonic acid (6:2 FTS) were the dominant PFAS in both the maternal and cord serum. The median ∑PFAS concentration was 14.18 ng/mL, and the ∑PFAS concentration was observed to decline from the first trimester to the third trimester. The transplacental transfer efficiencies (TTE) of 29 PFAS were comprehensively assessed, and a "U"-shaped trend in TTE values with increasing molecular chain length of perfluoroalkyl carboxylic acid (PFCA) was observed in this study. Moreover, the maternal concentrations of 9-chlorohexadecafluoro-3-oxanonane-1-sulfonic acid (6:2 Cl-PFESA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUdA), perfluorododecanoic acid (PFDoA), PFOS, and hexafluoropropylene oxide dimer acid (HFPO-DA) in the 2020 cohort were significantly lower than those in the 2018 cohort, declining by about 23.85-43.2% from 2018 to 2020 ( < 0.05). Higher proportions of emerging PFAS were observed in fetuses born in 2020. This birth cohort was collected during the COVID-19 epidemic period. The change in the PFAS exposure scene might be in response to the different exposure profiles of the 2018 and 2020 cohorts, which are attributed to the impact of COVID-19 on the social activities and environment of pregnant women. Finally, by application of a multiple informant model, the third trimester was identified as the critical window of vulnerability to PFAS exposure that affects birth weight and birth length.