The outer layer of the embryo, the trophectoderm (TE), is what starts building the placenta. TE cells turn into the early placental cell types that help the embryo attach, invade the uterine lining, remodel blood vessels, and begin producing hormones like hCG. This early development influences implantation, early pregnancy progression, and in some cases may relate to complications later in pregnancy.
Trophectoderm (TE): The outer layer of the blastocyst. These are the cells that eventually form the entire placenta. The fetus comes from the inner cell mass; the placenta comes from the TE.
Trophoblast: Once the embryo starts implanting, TE cells turn into โtrophoblastโ cells that are the early building blocks of the placenta.
Cytotrophoblast (CTB): A pool of dividing cells that act as the placentaโs โsource material.โ CTBs produce two major trophoblast types:
- Syncytiotrophoblast: A layer of cells that reaches into the uterine lining and produces early pregnancy hormones like hCG.
- Extravillous trophoblast: Invasive cells that move into the uterine lining, anchor the placenta and help open the maternal blood vessels so the pregnancy has enough blood flow.
Placenta: As syncytiotrophoblast and extravillous trophoblast cells expand and organize, they form the placenta, the organ responsible for nutrient exchange, hormone production, and supporting the pregnancy throughout pregnancy
Overall progression: TE โ trophoblast โ CTB โ syncytiotrophoblast and extravillous trophoblast โ placenta.