Abstract:
Human implantation and early placental development are crucial for on-going pregnancy success, but involve complex interactions between the specialized cells of the placenta (trophoblasts) and the maternal decidua that are not entirely understood. The blastocyst embeds itself within the decidua around 7 days post-fertilization, and the outer trophectoderm layer expands rapidly and differentiates into the specialized trophoblast lineages of the villous placenta. The syncytiotrophoblast covers the surface of the placental villi and is responsible for all nutrient and gas exchange, whereas extravillous trophoblasts grow out from the placenta and invade the decidua to remodel the spiral arteries into wide bore vessels capable of delivering an increased and constant blood supply to the placental surface as pregnancy progresses. This article covers the process of blastocyst implantation, the development of the early human placenta, and the regulation of trophoblast differentiation and invasion at the matern-ofetal interface.