1. Eventually, the syncytiotrophoblasts come into contact with maternal blood and form chorionic villi . 2. The chorionic villi comprise the majority of the functional placenta. 3. They often surround the cytotrophoblasts, reminiscent of their normal anatomical relationship in chorionic villi . 4. Chorionic arteries branch off the umbilical artery, and supply the capillaries of the chorionic villi . 5. Chorionic villi ( from the embryo ) on the embryonic pole grow, forming chorion frondosum.6. These structures, called the chorionic villi , carry the fetal blood supply often sampled in prenatal tests. 7. Several days later, chorionic villi in the forming placenta anchor the implantation site to the uterus. 8. The chorionic villi create a large surface to maximize the exchange that takes place between the two blood supplies. 9. The chorionic villi emerge from the chorion, invade the endometrium, and allow transfer of nutrients from maternal blood to fetal blood. 10. Expected contents include the embryo or fetus, as well as the decidua, chorionic villi , amniotic fluid, amniotic membrane and other tissue.
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