Exposure to and Transplacental Transfer of Per- and Polyfluoroalkyl Substances in a Twin Pregnancy Cohort in Korea.

Twin pregnancies involving assisted reproductive technology, particularly among older women, are considered to be high risk and vulnerable to chemical exposures. Per- and polyfluoroalkyl substances (PFAS) can cross the placenta and affect the fetus, but their transplacental transfer (TPT) is not well characterized for twin pregnancies. We employed a subset of twin pregnancies from the Ideal Breast Milk (IBM) cohort and measured the levels of PFAS and related chemicals in maternal (n = 78) and cord serum (n = 156) samples. L-PFOS and PFOA were detected at higher levels in maternal serum, with geometric means of 4.22 and 2.80 ng/mL, respectively, while the level of Br-PFHxS was higher in cord serum (0.29 ng/mL). Higher maternal PFAS levels were associated with the occurrence of maternal vascular malperfusion. Greater differences in cord PFAS levels between twin newborns were associated with higher maternal PFAS levels and an asymmetrical placental perfusion. The TPT ratio exhibited a U-shaped pattern with the number of carbons of PFAS, similar to a singleton pregnancy. Moreover, those with eight carbon atoms, i.e., 9Cl-PF3ONS, PFOA, and PFOS, showed different TPT efficiencies with respect to their structure and functional group. While the twin pregnancy does not appear to influence exposure levels or TPT efficiencies of PFAS and related chemicals, the consequences of the exposure warrant further investigations in this population.