The cells then fuse and immediately start to divide, so that after 4 days there is a mazz of cells called the blastocyst . This develops little fingerlike structures, known as chorionic villi, which are necessary for the embedding of the developing embryo. After 7 days, the embryo reaches the uterus. The villi start burrowing into the lining of the uterus, and the egg receives a new source of nutrition by opening into the mother's blood vessels. The mass of cells begins to form into a fetus and an amniotic sac.
Amniotic fluid is put into production, and the amniotic and chorionic membranes appear.
By the 2nd week after conception, the pregnancy is large enough to be seen by the naked eye. The ovary still contains the tiny corpus luteum, which is supporting the conception. I had a difficult time because people didn't understand how attached I could be so early and quickly. My husband hadn't really accepted it yet, so it was much easier for him. While he tries to be helpful, he doesn't understand.