Human chorionic gonadotropin (hCG) is secrete by the embryo early in pregnancy to keep the corpus luteum for dying. This positive feedback will maintain the corpus luteum, which secretes Progesterone and Estrogens throughout pregnancy, in order to keep the endometrium well to nourish the embryo/fetus.
Answer: I hope it helps!!
Explanation: I can't really explain on computer through a keyboard and stuff lol, but it's worked out. Please let me know if it's wrong :-)