ABSTRACT
The placenta is a fetal organ that early in gestation rapidly develops through a series of essential steps. These encompass
Anchoring of the placenta to the maternal decidua
Opening of uterine glands to enable nutrient supply of the embryo during the first trimester of pregnancy, prior to onset of maternal blood flow
Subsequent opening of spiral arteries to increase oxygen and nutrient supply to the fetus starting with the beginning of the second trimester
Establishing villous structures and the first primitive vascular plexus within the placenta independent of vasculogenesis within the embryo proper
Given the necessity to rapidly establish the uteroplacental vascular connection as well as the vasculature between embryo and placenta and because of the complex nature of the biological processes driving implantation, placentation, and embryo development, early gestation is a period of high vulnerability of both the placenta and embryo. Although tightly controlled by a variety of mechanisms, each of these processes can malfunction, which in certain situations may lead to impaired placental function later in pregnancy, which could manifest in pregnancy conditions such as preeclampsia and/or fetal growth restriction (FGR).