Diagram of anchoring villi (AV) at the maternal-fetal interface in normal and preeclamptic pregnancy

The floating villi (FV) are in the intervillous space in direct contact with the maternal blood. In normal pregnancy, invasive cytotrophoblasts (CTB) form cell columns (zone II/III) and invade maternal decidua and vasculature (zone IV). During the differentiation along the invasive path, the cytotrophoblasts dramatically alter their expression of various molecules, such as integrins. In preeclampsia, the invasive cytotrophoblasts fail to differentiate along the invasive pathway and do not gain access to spiral arteries.