A revised picture of extravillous trophoblast invasion

Extravillous trophoblasts (EVTs) invade the decidual stroma (interstitial trophoblast) and thereby attach the placenta to the uterus. They also invade toward spiral arteries (endovascular trophoblast) for the establishment of the uteroplacental blood flow. The latter does not start before the end of the first trimester of pregnancy. A new type of extravillous trophoblast invading into uterine glands (endoglandular trophoblast) has been described recently opening uterine glands toward the intervillous space of the placenta to enable histiotrophic nutrition. This review gives an overview about the different subtypes of EVTs and presents novel peculiarities in the field of EVT invasion. EVTs invade more structures in the maternal decidua than previously assumed. Especially a proper invasion of uterine glands by endoglandular trophoblasts may have more impact on the outcome of pregnancy than assumed so far.