Trophoblast Development in the First Trimester of Pregnancy

The placenta is the exchange organ that regulates metabolic processes between mother and the developing fetus. In the first trimester, after blastocyst implantation, the extravillous cytotrophoblast erodes the vascular walls of the maternal spiral arteries and enters their lumen [1]. This event creates wide uteroplacental arteries able to supply the growing fetus with the blood flow required [2,3]. During the first weeks of pregnancy, the extravillous cytotrophoblast cells are so voluminous that they plug the spiral arteries, creating a low oxygen environment which is essential for correct placental development