Embryo Transfer is the final step in the In Vitro Fertilization (IVF) process during which the created embryo is implanted in the uterus. Typically, embryos are transferred when they consist of two to eight cells. While the transfer may take place anytime between days 3 and 6 after egg retrieval, most often the embryo transfer is performed between days 3 to 5. In some cases, the embryo is more frequently transferred into the uterus of the woman who provided the egg for IVF, but in some situations may be implanted in a surrogate. The rate of success in embryo transfers, that is, embryo transfers that result not only in pregnancy, but in a live birth, is variable, most commonly affected by the age of the mother who provided the egg. Generally speaking, the success rate hovers around the 50 percent mark.
The Embryo Transfer Procedure
With the patient in a relaxed state, the doctor uses a catheter to deposit a predetermined number of embryos in the uterus, gaining access through the vagina. The correct placement of the embryos near the top of the endometrial cavity is important so ultrasound technology is used for guidance. The procedure is a very delicate one, involving no unnecessary manipulation of the embryos. Even with the most careful embryo transfer, the success of the procedure is chiefly dependent on the genetic quality of the eggs.
Once the embryos are implanted, the patient remains at rest on her back for at least an hour and is usually directed to rest for the next 48 hours. Doctors differ in their advice regarding optional activity levels for their patients after this period since there is no evidence that normal activity affects implantation but the procedure is most often painless. Patients trying to conceive through In Vitro Fertilization (IVF) are administered supplemental progesterone and estrogen, both to assist in conception and to sustain the pregnancy. A woman who has undergone an embryo transfer continues to take hormones as a supplement for several weeks after her pregnancy has been confirmed and usually until the placenta takes over the hormone production.
Complications of an Embryo Transfer
The decision regarding the number of embryos that should be transferred in a complicated one surrounded by a certain amount of controversy. While increasing the number of embryos transferred increases the possibility of a resulting pregnancy, it also increases the chance of a multiple pregnancy which are riskier than single ones both for the mother and the offspring.
Fresh Embryos vs. Frozen Embryos
Typically, more fresh embryos are created than will be transferred during a single procedure. The remanding embryos or the most viable of them are frozen for future use in a process called frozen embryo transfer, or FET. The original freezing process was relatively slow and has a lower rate of success than the method currently used known as vitrification. Vitrification freezes the embryos so quickly that ice crystals do not have time to form and as a result, less cell degeneration occurs. Where fresh embryo transfer used to have a 10 percent higher rate of success than FET, recent statistics show the two methods as now essentially on a par.
Frozen embryos may be used when the first embryo transfer has been unsuccessful or for another potential pregnancy for the same couple later on. Another option is that the frozen embryos may be donated to another couple or single woman with infertility problems. Because the embryos are encased during freezing in a liquid know as a cryoprotectant, they are visible for about a decade. Even so, not all frozen embryo survive the thawing process, so more embryos are usually thawed than will be transferred.
Risks of an Embryo Transfer
The risks of an embryo transfer are minimal. These risks include loss of embryos during transfer or incorrect placement of the embryos. In some cases the embryos may be mistakenly implanted in one of the fallopian tubes.