Implantation is the process by which the early embryo attaches and then imbeds itself into the uterine wall, allowing for the formation of the placenta and eventual growth of the fetus. This is one of the most sophisticated and delicate procedures in human reproduction. Hundreds of highly specialized proteins are involved in complex interactions with each other. These proteins, as well as other molecules, help the fetus get access to maternal vessels without causing a break down of the maternal vascular integrity. The embryo literally perforates the maternal uterine vessels and destroys their muscle fibers, reducing the resistance of these vessels to almost zero and thus assuring continuous and uninterrupted blood supply to the fetus. Failure in this process can lead to all sorts of placental malfunctions, which may in turn lead to some of the most serious prenatal complications ranging from fetal brain damage to pregnancy loss.