Fig. 1

The placental barrier. Schematic representation of the human placental structure in term pregnancy. From the chorionic plate, the umbilical cord and chorionic villi originate. The intervillous space is filled with maternal blood entering via remodeled maternal spiral arteries and leaving via the uterine veins. The syncytiotrophoblast, which is formed by the fusion of cytotrophoblasts, faces the maternal blood and therefore constitutes the first layer to get into contact with systemic DEPs. While a complete cytotrophoblast layer exists in early pregnancy, these cells are sparse at the end of pregnancy. Beneath this syncytium lay the villous stroma containing fibroblasts and placental macrophages (i.e., Hofbauer cells) and the endothelial cell-lined fetal microvessels. Created with BioRender.com