Frozen Embryo Transfer (FET)
Frozen/thawed embryo transfer (FET) is a treatment that involves implanting embryos that were retrieved from the patient during a previous IVF cycle and held safely in a frozen state.
About Frozen Embryo Transfer
The Center for Human Reproduction (CHR) routinely performs successful Frozen Embryo Transfers. One advantage of FET is reduced cost. When frozen embryos are available from a previous IVF treatment, subsequent implantations can be accomplished at a savings. The savings reflects the fact that IVF cycles with cryopreserved and thawed embryos are less involved and thus less costly than generating fresh embryos with a new IVF cycle.
Advantages of Frozen Embryo Transfer
For a similar reason, some patients find that preparing for a frozen embryo transfer involves less medication and may be easier than an IVF cycle. However FET treatments still require patients to take medications (hormones) to build the uterine lining to prepare to receive the embryos. (For more about specific treatment details, see CHR's Patient Education primer for FET treatments that also includes details of recommended medications.)
Frozen Embryo Transfer Treatment Procedures
The duration of FET treatments vary by patient; in general, most patients fall into the three- to four-week range. The number of embryos transferred depends on several factors: patient age, embryo quality, and the number of embryos available after the thawing process. Again, speaking in general terms, our fertility experts prefer to thaw one more embryo than was transferred in the fresh cycle.
Embryos are thawed individually until there are enough available to complete the transfer process as described above. For example, if a patient needs three embryos transferred, initially three will be thawed, and depending on the survival rate, more will be thawed until three viable embryos are obtained. Embryos will be allowed to grow out one or two days after thaw.
Embryos are grown for several days before they are cryopreserved for later use, however may be frozen at any point after fertilization. Indeed, there is general consensus that cryopreservation (freezing) is possible at any stage of embryo development. However while embryos frozen immediately after fertilization, demonstrate capacity to survive the thawing process, the embryos that prove most successful for achieving implantation are allowed to develop in the lab for a day or two prior to the cryopreservation process.
It is difficult to know how many thawed embryos will reach the stage of development desired by the physician for transfer. Therefore, a higher number of embryos must be thawed. If a large number of embryos does reach that stage of development, then there is a dilemma. Either a larger number of embryos must be transferred (which increases the risk of multiple pregnancy) or the extra embryos must be discarded or refrozen.
Frequently Asked Questions about FET
Often we are asked if embryos can be re-frozen. The answer is yes. However this is not an ideal scenario, as each thawing and freezing cycle includes the risk for damage – albeit a minor one. Though, the more cycles an embryo is subjected to, the more often it is exposed to risk.
Embryos can remain frozen indefinitely. CHR maintains a state-of-the-art storage facility for which there are annual fees. In general, couples use their frozen embryos within a few years, though we have had couples return after as long as ten years. CHR regularly publishes the latest data for success rates related to Frozen Embryo Transfer.
Last Updated: November 15, 2014