- What is FET
- General Trends with FET Success Rate
- Factors that Impact FET Success Rate
- Who Benefits from FET?
- How to Improve the Success of FET
What is FET
FET stands for frozen embryo transfer. In in vitro fertilization (IVF) treatment, patients who have had previous rounds of IVF resulting in healthy embryos that were frozen can opt to use those frozen embryos instead of fresh ones.
FET reduces costs significantly, and in some cases, increases the chances of success. The reason is that frozen embryos are already viable and fertilization has already occurred. In a brand new IVF cycle with no frozen embryos, fertility doctors must retrieve eggs, fertilize them with sperm, and then transfer. At any point in that process, IVF could fail. For example, some rounds of IVF result in no viable eggs to fertilize. Another round of IVF may result in no fertilized or healthy embryos.
So when a fertility specialist retrieves multiple viable eggs which are subsequently fertilized, the clinic will suggest that patients freeze those embryos for later use, in the event the transfer is unsuccessful and another round of IVF is needed.
When patients use frozen embryos, they can skip the egg retrieval and fertilization process, saving thousands of dollars in medication and treatment costs.
In IVF using fresh embryos, the cycle consists of the following common steps:
- Cycle suppression
- Ovarian stimulation
- Egg and sperm retrieval
But in FET cycles, none of the steps prior to transfer other than cycle suppression are required. Fertility specialists will administer suppression medication and may administer some medications to thicken and improve the uterine lining, but other than that, the majority of IVF procedures are eliminated.
A typical FET procedure consists of the following steps:
- Lupron administered to suppress cycle on Day 21
- Estrogen administered approximately 10 days later
- Progesterone administered 14 days later; Lupron stopped
- Embryo(s) thawed and transferred 7 days later
Much of the process involved with FET concerns timing and preparation for transfer. Egg retrieval and fertilization have already been done, which is beneficial. The potential for failure lies primarily with thawing – not all embryos survive the thaw.
While all clinics are different, FET cycles can cost around $4,000 total, including medications and transfer. Considering that the average cost of a round of IVF with fresh embryos is $12,000, FET dramatically cuts costs.
General Trends with FET Success Rate
Fertility clinic data suggests that the FET success rate are similar to the success rate of a fresh IVF cycle. In other words, they are not significantly higher or lower if you consider one round at a time. However, in some cases, FET increases the chances of success in multiple rounds of IVF.
Some clinics quote the chances of success per FET as high as 60% in women aged 35 or younger.
The most important thing to consider is the age of the mother at the time the eggs were retrieved and fertilized before freezing. That is the primary variable in success rate. Regardless of how much time has passed, the mother’s age at egg retrieval is what impacts success rate, along with the health and viability of the egg and sperm.
Considering that egg quality and quantity both decrease with age, some patients opt to freeze extra embryos in the first few rounds of IVF. This increases their chances of success later, in the event that IVF fails in the initial rounds.
Factors that Impact FET Success Rate
The number of healthy embryos that are successfully frozen AND successfully thawed impacts FET success rate. Typically, people tend to forget that embryos must not only survive the freezing process, but they must also survive the thawing process and then survive the transfer.
All of that processing impacts embryos and only the strongest survive it. If none of the embryos survive thawing, FET fails.
Patients typically have a choice about testing and evaluating the quality of embryos. Some may choose to have all of them tested prior to freezing, while other patients will wait until another round of IVF is deemed necessary, first. Cost typically impacts that choice, as testing adds additional cost to the round.
If thawed embryos are subsequently tested and determined unfit for transfer, the chances of success sharply decline. For this reason, many patients opt to test the embryos before freezing. The only major issue with testing prior to freezing is that some embryos may be damaged in the process of testing.
As stated earlier, the mother’s age at the time of egg retrieval impacts success rate of frozen or fresh IVF rounds. This is the primary contributing factor, as age impacts both quantity and viability of the embryos.
Age of Embryo (Day 3 vs Day 5)
Some research suggests that older embryos (Day 5 embryos called Blastocysts) have a greater chance of success than zygotes (Day 3 embryos). Blastocysts have survived longer and are further along in development, and that is one of the reasons success may be higher.
Freezing Method and Clinical Procedures
Embryos are extremely fragile and do not live long outside of the uterus. In IVF, the way clinics freeze and thaw embryos has a major impact on IVF success in the present and future. Recent freezing methods improve the chances of survival after thawing. Additionally, clinics must use near exact timing strategies when testing, freezing, thawing, and transferring, to ensure embryos have the best chance for survival.
Who Benefits from FET?
Because of the significant cost savings as well as the increased chances of success, any patient with extra healthy embryos benefits from frozen embryo transfer. While there are ethical concerns with freezing embryos for too long or discarding them, many patients benefit from the option to freeze them.
Older women benefit in significant ways because rounds of IVF treatment for older women can be extremely costly. FET can eliminate the risk and cost associated with egg retrieval. At the very least, frozen embryo transfer benefits older women over 40 success by reducing the need for powerful medications to stimulate the ovaries and produce viable eggs.
Women with low ovarian reserve – regardless of age – also benefit from FET, for the same reasons older women do. Each round of IVF that involves egg retrieval and fertilization is risky and expensive. Using frozen embryos that are healthy and have already been tested and evaluated, fertility specialists have a much greater chance of success.
Lastly, women at risk for OHSS (ovarian hyperstimulation syndrome) benefit from FET, because it eliminates the ovarian stimulation process. OHSS occurs as a result of medications that stimulate the ovaries, and that part of the IVF process is unnecessary in a round that uses frozen embryos.
Likelihood of Embryos Available for Freezing
The most critical factor to IVF success is a healthy egg. Second to that is a healthy embryo. Not all IVF rounds result in extra embryos that can be frozen. Some embryos may not survive long enough, and some may have abnormalities and cannot be kept. Fertility specialists will likely test the embryos before freezing them (however, in some cases they can be thawed later and tested before transfer). Any that are not viable will not be frozen.
Egg quality certainly impacts the likelihood of having enough healthy embryos that there are extras to freeze. Additionally, some patients may ask the doctor to transfer all of the embryos. So the number of embryos available to freeze is going to vary from patient to patient.
Another factor in availability is that specialists will always choose the healthiest, most viable embryos for transfer and then choose which to freeze from the remaining ones. That means that the frozen embryos are not the best – they were not the healthiest of the group. However, in almost all circumstances, clinics will not freeze unhealthy embryos. So a patient can be secure in knowing that frozen embryos are viable and healthy enough for transfer later.
Handling Extra Embryos: Option for Frozen Embryo Adoption
If there are ethical concerns about extra embryos, unused frozen embryos can be donated to clinics or adopted by other patients. The National Embryo Donation Center facilitates embryo adoption, which is a process where couples donate their unused frozen embryos to another infertile couple to use. This way, embryos are not wasted or discarded, and couples who haven’t had success with egg retrieval or fertilization have a much greater chance of having a baby.
How to Improve the Success of FET
Unlike fresh embryo transfer, frozen embryo transfer success can be greatly increased or decreased by handling. Frozen embryos go through much more than fresh embryos do.
Clinics can improve the chances of success of FET with proper timing and handling. Patients, on the other hand, can potentially increase FET success rate by freezing healthy embryos early in the process of IVF. If a patient has two healthy embryos, instead of transferring both, she may opt to transfer them in separate rounds of IVF.
If both are transferred, neither may result in pregnancy, or it may result in a risky multiple pregnancy. But if only one is transferred at a time, the patient will not have to go through stimulation, egg retrieval, or fertilization, and each transfer has an equal chance of success.