Extravillous trophoblast

Extravillous trophoblasts (EVTs), are one form of differentiated trophoblast cells of the placenta. They are invasive mesenchymal cells which function to establish critical tissue connection in the developing placental-uterine interface. EVTs derive from progenitor cytotrophoblasts (CYTs), as does the other main trophoblast subtype, syncytiotrophoblast (SYN). They are sometimes called intermediate trophoblast.

EVTs that derive from CYT cells on the surface of placental chorionic villi that come into contact with the uterine wall - at the placental bed - begin to express the HLA-G antigen. Extravillous trophoblast (EVT) cells migrate from anchoring villi, and invade into the decidua basalis. Their main function is remodelling the uterine spiral arteries, to achieve an increase in the spiral artery diameter of from four to six times. This changes them from high-resistance low-flow vessels into large dilated vessels that provide good perfusion, and oxygenation to the developing placenta. When invasion is shallow it is inadequate, the arteries remain narrow at their openings into the intervillous space, and is the cause of pre-eclampsia, fetal growth restriction and still birth.

EVT are a low-incidence (<5% of trophoblasts), but critical and multifunctional, subtype of trophoblast in the placenta.