The blastocyst is moved by contraction of the uterine tube and cilia movement into the uterus, where it undergo a continuous cell division for 2-4 days before becoming implant in the endometrium at around 2 weeks after fertilization and then it is called an embryo. After 10 weeks or so of embryonic development , the embryo known as fetus.
Before implantation blastocyst start to secretes hormone and proteolytic enzymes which lead to degeneration of neighboring endometrial cells results in forming small cavities. This cavities become filled with blood and within 9 days following fertilization the trophoblast cells begin to secret human chorionic gonadotropin (hCG) which is reach to a peak at 7-12 weeks and then decline. HCG binds to LH receptors and prevents the degeneration of the corpus luteum which is keep to secret estrogen and progesterone.