Implantation and Embryo Support
In the natural process of fertilization, the lining of the uterus is made ready for implantation by a small cyst on the ovary called the corpus luteum. The corpus luteum actually arises from the ruptured follicle. The hormone progesterone is produced by the corpus luteum and helps to keep the lining of the uterus prepared for implantation of the embryo(s).
Because some of the cells which make progesterone may have been aspirated or disrupted during the retrieval and the drugs used for stimulation may alter their function, it is necessary to provide supplemental progesterone. Therefore, daily administration of progesterone will begin after the retrieval.
The embryos do not implant until approximately two to three days after a Day 3 transfer or one day later for a blastocyst transfer. There are many factors that affect the ability of the embryo to implant, including normality of the embryo and the receptivity of the endometrium.