Frozen Embryo Transfer (FET) Procedure

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A frozen embryo transfer, or FET, is a kind of IVF treatment where a cryopreserved embryo created in a full IVF cycle is thawed and transferred to a woman’s uterus. The cryopreserved embryo may be from a woman’s previous conventional IVF cycle, or it may be a donor embryo. If a donor embryo is being used, the embryo is not genetically related to the woman or her partner. 

Most of the time, a frozen embryo transfer takes place when there are “extra” embryos after a conventional IVF cycle. A “fresh” transfer is usually preferred. However, some doctors are recommending elective frozen embryo transfer—also referred to as a “freeze all” approach—where a fresh transfer is not attempted. In this case, all embryos are cryopreserved and transferred in a FET cycle in the next month or so.

Why Choose Frozen Embryo Transfer?

You may choose to have a FET-IVF cycle due to the following conditions and circumstances.

You Have Extra Embryos

You may have cryopreserved embryos after a fresh IVF transfer fails. During IVF one or several embryos may result. But it's only safe to transfer one or two at a time. Transferring multiple embryos increases the risk of a high-order multiple pregnancy (like triplets or quadruplets.) To reduce this risk, some doctors recommend an elective single embryo transfer (eSET) in patients with a good prognosis.

Sometimes, there are “extra” embryos after an IVF cycle. Most people choose to freeze or cryopreserve their extra embryos.

For example, let’s say you get five embryos. Let’s also say your doctor recommends elective single embryo transfer for you. This would mean that one embryo will be transferred, and the four others will be cryopreserved.

If the one embryo transferred doesn’t result in a successful pregnancy, you have two options. You can do another fresh, full IVF cycle, or you can transfer one or two of your previously cryopreserved embryos. The most cost-effective option would be to transfer one of your previously frozen embryos. This is what many couples will choose to do.

You Want Another Child

You may want to give your IVF-conceived child a sibling. If your fresh embryo transfer resulted in pregnancy, you may have embryos still waiting in cryopreservation. Cryopreserved embryos can remain on ice indefinitely.

In the future, you may decide to do a FET-IVF cycle to give your child a sibling. Your other option would be to do another fresh cycle and not use your cryopreserved embryos, but as previously mentioned, this is a more expensive route.

You're Using Genetic Screening

Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are assisted reproductive technologies that allow embryos to be screened for specific genetic disease or defects. This is done by biopsying the embryo on day three or five post-fertilization, post egg retrieval.

Sometimes, the results get back in time to do a fresh embryo transfer. However, if a day five biopsy is done, or the genetic testing is complex and requires more time, then all embryos biopsied are cryopreserved. Once the results come back, decisions can be made on which embryos to transfer. These would be FET-IVF cycles.

You Choose an Elective Procedure

You might choose elective frozen embryo transfer, with or without pgd/pgs. Also known as a “freeze all” protocol, this is when a fresh embryo transfer isn’t part of the plan at all. This may occur with PGD/PGS, but it can also be done without genetic screening.

There is a theory that the fertility drugs that stimulate the ovaries best don’t necessarily create ideal implantation conditions in the uterus. This means that a fresh transfer may be less likely to result in a healthy, ongoing pregnancy.

To avoid this problem, three to five days after egg retrieval, all embryos are cryopreserved. The next month or in the month after, when the endometrium has had a chance to form without the influence of ovarian stimulating drugs, a frozen embryo transfer can take place.

During that FET cycle, your doctor may prescribe hormonal medications to enhance endometrial receptivity. This is especially true if you don’t ovulate on your own. Or, your doctor may do the FET as a “natural” cycle, with hormonal medications used. (More on this below.)

You're at High Risk of OHSS

Ovarian hyperstimulation syndrome (OHSS) is a risk of fertility drugs that can in severe (but rare) cases lead to loss of fertility and even death. If your risk of OHSS appears high before a fresh embryo transfer can take place, it may be canceled and all embryos cryopreserved.

Cancellation may happen because pregnancy can exasperate OHSS. It may also take longer to recover from OHSS if you’re pregnant. Once you’ve recovered from OHSS, a frozen embryo transfer cycle can be scheduled.

Fresh Embryo Transfer Canceled

Fresh embryo transfer can also be canceled for other reasons. Your fresh transfer may need to be canceled if you get the flu or another illness after egg retrieval but before transfer. Also, if the endometrial conditions don’t look good on the ultrasound, your doctor may recommend cryopreserving all embryos. At a later date, you can schedule a FET-IVF.

You’re Using an Embryo Donor

Some couples choose to donate their unused embryos to another infertile couple. If you decide to use an embryo donor, your cycle will be a frozen embryo transfer. 

Which Method Is Best?

Some studies have found that pregnancy rates are better with frozen embryo transfers than with fresh embryo transfers. Studies have also found that pregnancies conceived after frozen embryo transfer may have better outcomes for the baby. Most studies have been done in younger women with a good prognosis, so it’s unclear what it would mean for those over age 35 or with a poor prognosis.

More research needs to be done. However, if it proves to be true that FET-IVF is more likely to lead to a live birth than a fresh transfer, what could be the reason for it?

One possible theory is that the fertility drugs that are ideal for ovarian stimulation are less than ideal for endometrial formation. This means that stimulating the ovaries in one cycle—with a plan to transfer the embryos during a non-stimulating cycle—may be better for implantation.

The second possible reason could be that embryos that survive cryopreservation are stronger. Weaker embryos may not survive the extended time in the lab and the freeze-thaw process. This is one of the risks you take when choosing frozen embryo transfer. However, some doctors argue that those less-strong embryos wouldn’t have led to a healthy pregnancy in any case.

You may have read about earlier studies, which compared fresh vs. frozen transfer. Many of these older studies concluded that fresh embryo transfer cycles had better pregnancy rates than frozen embryo transfers. However, that research can’t be applied to a “freeze-all” cycle.

The older studies involved taking the less-than-ideal embryos, freezing them, and transferring the best-looking embryos right away. It’s logical that the less-than-ideal embryos would have lower success rates than the good-looking ones that were transferred in a fresh cycle.

What to Expect

There are two basic kinds of FET-IVF cycles: hormonal support cycles and “natural” cycles. The most commonly performed FET-IVF cycle is a hormonally supported cycle. This is because the day of transfer is easier to control (making it easier for the fertility clinic and lab), and because hormonal support is needed if there are female ovulatory problems.

FET With Hormonal Support

A FET-IVF cycle with hormonal support starts at the end of the previous menstrual cycle, much like a conventional IVF cycle. Injections of a drug meant to control and shut down the reproductive cycle are given. Usually, the GnRH agonist Lupron is used, but other pituitary-suppressing medications may be chosen instead.

Once you get your period, a baseline ultrasound and blood work are ordered. If all looks good, estrogen supplementation is started. This is to help ensure a healthy endometrial lining. Estrogen supplementation is continued for about two weeks. Another ultrasound and more blood work are ordered. The monitoring during a FET-IVF cycle is significantly less than during a conventional IVF cycle.

After approximately two weeks of estrogen support, progesterone support is added. This may be via progesterone in oil injections or possibly with vaginal suppositories. The embryo transfer is scheduled based on a) when progesterone supplementation was started, and b) at what stage the embryo was cryopreserved.

For example, if the embryo was cryopreserved on day 5 post-egg-retrieval, then the frozen embryo transfer will be timed for day 6 after progesterone supplementation starts.

FET Natural Cycle

With a FET natural cycle, medications aren’t used to suppress or control ovulation. Instead, the embryo transfer is scheduled based on when ovulation naturally occurs. The timing of the embryo transfer is crucial. It must occur a particular number of days after ovulation. As mentioned above, that day will depend on whether the embryo was frozen on day 3 or day 5 post-egg retrieval.

Because timing is essential, the cycle is closely monitored either at home with ovulation predictor tests or at the fertility clinic with ultrasound and blood work. Since ovulation predictor kits aren’t always easy to interpret, most doctors rely on ultrasound and blood work to time the transfer. When ovulation is detected, progesterone supplementation is started, and the transfer date is scheduled.


A frozen embryo transfer cycle has significantly fewer risks than a full IVF cycle. One of the primary risks to IVF (and fertility drugs) is ovarian hyperstimulation syndrome (OHSS). However, you don't need to worry about OHSS in a FET cycle since ovarian stimulating drugs aren't used. 

Depending on how many embryos are transferred, there is a risk of multiple pregnancy. Even twin pregnancies come with an increased risk to the mother and babies. Embryo transfer comes with a slightly increased risk of ectopic pregnancy. There is also a very small risk of infection.

With cryopreservation, some embryos may not survive the freeze and thaw process. With elective frozen embryo transfer, this means you may lose embryos that would have been available if you had done a fresh transfer. 

There is a possible increased risk of babies being born “large for gestational age” from frozen embryo transfers. But a meta-analysis found that pregnancies and babies from frozen embryo transfers may, in fact, be healthier than those from fresh embryo transfers. Frozen embryo transfer babies were at:

  • Lower risk for low birth weight
  • Lower risk of preterm birth
  • Lower risk of stillbirth

One study compared the risks of a birth defect in fresh IVF transfers, frozen embryo transfers, and naturally conceived children. The study found that children were three times more likely to have the birth defect with fresh IVF transfers when compared to naturally conceived children. However, that increased risk wasn't seen with frozen embryo transfer. The overall risk of birth defects was still very low.


The average cost for a frozen embryo transfer is between $3,000 and 5,000. This includes monitoring, any hormonal support, and the transfer process itself. A natural cycle would cost slightly less, eliminating the cost of fertility drugs. This price does not, however, include the ​expenses from the initial IVF treatment, nor the initial cryopreservation of the embryos or storage fees.

When talking to your doctor about costs, make sure the price they quote includes everything so that you can plan your budget accordingly. 

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