Phase 4: Phase four is the actual embryo replacement. This is usually quite straightforward. The embryo(s) are drawn into a soft plastic catheter, which is placed through the cervix into the uterus, sometimes with ultrasound guidance, so that the embryo can be delivered to its natural home in the uterus. No anesthesia is necessary. Hormonal values may be checked over the next week, and frequently progesterone supplements are given as injections, vaginal suppositories, vaginal gels, and less commonly by mouth. A pregnancy test usually is done 12-14 days after retrieval (Phase 2).
IVF technology has allowed development of egg donation programs whereby women with poor or absent ovarian function can become pregnant using eggs from a healthy young woman. Women who have ovarian function, but who lack a uterus or who have a uterus that is reproductively incompetent, may supply eggs to be fertilized and placed in a recipient's uterus. Known as "carrier gestation," this type of pregnancy is initiated with husband and wife both having genetic input. This is different from surrogate parenting, in which a surrogate mother is inseminated with the sperm from the husband of the patient so that the surrogate mother supplies the eggs.
Sometimes, dependent on egg quantity, quality, and sperm function, we have more embryos than can reasonably be returned to the uterus. These embryos can be frozen (cryopreserved) in liquid nitrogen, probably for an indefinite period of time. In actual practice, if pregnancy has not occurred from the “fresh” transfer of embryos, the stored embryos can be thawed for replacement in the next cycle without the need for stimulation and all the hormonal monitoring. This is referred to as "frozen-thawed replacement."
Additionally, a couple who wants another child can return for frozen-thawed replacement several years after a successful delivery from previous IVF. Studies have shown that the freeze-thaw process does not introduce any increased risk of malformation in the offspring. Embryos can be frozen and thawed with fair success, and sperm has been stored for years and used later. Storage of eggs, however, is quite another matter. We are still in the early learning phases of how to successfully accomplish this. Banking of eggs would allow women facing chemotherapy that might permanently destroy ovarian function to have a reproductive option at a later date, and would also allow women to initiate pregnancy later in life when career and development goals have been satisfied.
Some men have a low enough sperm quality such that standard IVF is not sufficient to induce pregnancy. Intracytoplasmic sperm injection (ICSI) is an IVF technique that involves drilling a small hole through the outer membranes of the egg (oocyte) and introducing a single sperm into the interior (cytoplasm) of the egg with a hollow glass needle. This technique overcomes most of the sperm abnormalities that prevent normal fertilization.
In some men, no sperm are present in the ejaculate produced during intercourse or masturbation but sperm are, in fact, produced in the testes and are blocked from reaching the outside world. This may be due to the lack of development of a duct which carries sperm from the testes to the penis, previous infection or surgery, or because sperm production is extremely limited. Immature sperm can be extracted from the testes with a needle under local anesthesia and injected into an egg using ICSI to achieve pregnancy. Some cases of poor sperm quality involve a genetic sperm problem that can be passed on to a son, so genetic screening of the parents may be needed.