Exposure to per- and polyfluoroalkyl substances in women with twin pregnancies: Patterns and variability, transplacental transfer, and predictors.

The extensive exposure to per- and polyfluoroalkyl substances (PFASs) has raised public health concerns. The issue of PFAS exposures in women with twin pregnancies remains unresolved. To determine exposure profiles, the transplacental transfer efficiencies (TTEs) of PFASs and predictors were estimated. We found that serum PFASs were widely detected, with detection rates of over 50% for 12 PFASs in maternal serum throughout pregnancy. The majority of PFAS levels exhibited fair to good reproducibility (ICCs > 0.40). Moderate to low correlations were observed for most PFASs between twin cord serum and maternal serum at three trimesters (rs = 0.13-0.77, p values < 0.01). We first presented a U-shaped trend for TTEs with increasing chain length for perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) in twins, even in twin sex subgroups. Further, we found that PC4 and PC5 (indicators of exposure to PFHxS and 6:2 Cl-PFESA) were positively associated with age (ß = 0.85, 1.30, and 1.36, respectively). Our findings suggested that there is moderate variability among certain PFASs and that these PFASs have the ability to cross the placental barrier. Exposure patterns were found to be associated with maternal age.