After fertilization, the blastocyst implants in the uterine wall. This process when the blastocyst attaches to the uterine walls days after ovulation is called implantation. Once blastocyst implants onto the uterine wall, the trophoblast secretes HCG, which stimulates the corpus luteum to secrete estrogen and the progesterone, which suppresses menstruation. The trophoblast will develop a membrane called the chorion which will take over for the corpus luteum.
