Preparation Of The Recipient For Embryo Transfer
In order for embryos to implant into the recipient’s uterus, the endometrium (uterine lining) must be prepared and synchronized with the donor reproductive cycle. Numerous methods of endometrial preparation have been described; however, the principle of hormonal preparation is similar. Women who have ovarian function are given a GnRH-a to temporarily suppress their menstrual cycle. When the donor starts her hormonal medications to stimulate her ovaries, the recipient is given estradiol to stimulate the endometrium to develop. Estradiol may be given in the form of an oral pill, transdermal patch, or injection. Ultrasound assessment of the endometrium and blood tests may occur during this time. The recipient begins progesterone on the day after the donor receives hCG. Progesterone causes specific maturational changes within the endometrium that enable the embryo to implant. Progesterone may be given by intramuscular injection, vaginal gel, or tablet.
Embryos are transferred into the recipient’s uterus, usually within three to five days after the eggs are fertilized in the laboratory. The embryo transfer (Figure 2) is performed by placing a small catheter with the embryos through the cervix and into the uterus. If the recipient couple has extra embryos, these embryos may be cryopreserved (frozen) for use at a later time in additional attempts to achieve a pregnancy.
The hormonal replacement regimen of estradiol and progesterone is continued until the recipient achieves a positive pregnancy test. If the pregnancy test is positive, estradiol and progesterone are continued through the first trimester to support the early pregnancy.