Frozen Embryo Transfer (FET) Procedure

A frozen embryo transfer (FET) is a type of IVF treatment in which a cryopreserved embryo created in a previous egg retrieval cycle is thawed and transferred to the uterus. Often, FET uses frozen embryos a gestational parent has from a previous conventional IVF cycle. A cryopreserved embryo can also be a donor embryo.

There are many possible ways to use donor embryos as a part of FET. Options include full embryo donation, the donation of an egg that can be inseminated with a partner's sperm and then frozen, or the donation of sperm that can be inseminated into a partner's egg and then frozen.

Frozen vs. Fresh Embryo Transfer

A "fresh" embryo isn't necessarily preferred, but it can be helpful in some cases. For example, fresh embryos may be recommended for younger patients when there is not a suspected chromosomal issue or in older patients who have embryos that might have a better chance in utero without waiting for genetic tests (sometimes embryos used in genetic testing have to be frozen).

Research shows that success rates are nearly identical with fresh and frozen embryos. Some studies show a small advantage to fresh embryos, but the difference tends to be negligible. Plus, other studies show a slightly higher accumulative live birth rate when frozen embryos are used under certain circumstances.

Some doctors recommend 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. Cryopreservation offers a viable way to store and preserve embryos for future use.

Why Choose Frozen Embryo Transfer?

If you have certain health conditions, other pertinent circumstances, or lifestyle considerations, your doctor may suggest FET to help you get pregnant.

You Have Extra Embryos

One or several embryos can result from IVF, 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, your doctor might recommend an elective single embryo transfer (eSET) if you have a good prognosis. Whether or not this transfer is successful, you may have embryos remaining after the cycle.

You might choose to freeze or cryopreserve any extra embryos after your IVF cycle in order to give yourself more options later.

For example, let’s say you get five embryos and your doctor recommends elective single embryo transfer for you (one embryo will be transferred and the four others will be cryopreserved).

If the transferred embryo doesn't result in a successful pregnancy, you have several options. These include doing another fresh, full IVF cycle or transferring one or two of your previously cryopreserved embryos. Often, the most cost-effective option would be to transfer one of your previously frozen embryos.

You Want Another Child

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

You're Using Genetic Screening

Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are assisted reproductive technologies that screen embryos for specific genetic diseases or defects. This is done through a biopsy on day three or five post-fertilization, post-egg retrieval.

Sometimes, the results from genetic screening and testing 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, all embryos that were biopsied will be cryopreserved. Once the results come back, your doctor can decide which embryos to transfer for an FET-IVF cycle.

You Choose an Elective Procedure

Some researchers have theorized that the fertility drugs that are best for stimulating the ovaries do not necessarily create ideal implantation conditions in the uterus. This could mean that a fresh transfer may be less likely to result in a viable, healthy pregnancy than using a frozen embryo at a later time.

With the “freeze all” protocol, all embryos are cryopreserved three to five days after egg retrieval. 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 (especially if you do not ovulate on your own). Your doctor might do the FET as a “natural” cycle, with hormonal medications used.

You're at High Risk of OHSS

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

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

Your Fresh Embryo Transfer Was Canceled

Fresh embryo transfer might also be canceled for other reasons. For example, you might not be able to have FET if you get the flu or another illness after egg retrieval but before transfer. Additionally, if the endometrial conditions do not look good on the ultrasound, your doctor may recommend cryopreserving all embryos, then scheduling FET-IVF for a later date.

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 marginally better with frozen embryo transfers than with fresh embryo transfers. Other research has indicated that pregnancies conceived after frozen embryo transfer may have better outcomes.

However, most studies have been done in younger women with a good prognosis. So it's unclear what results people over age 35 or with a poor prognosis could expect.

More high-quality research is needed to determine whether FET-IVF is more likely to lead to a live birth than a fresh transfer, and if so, what the reasons might be. Additionally, personal factors relating to your specific medical diagnosis can help determine which method is best in your case.

Another consideration is that the embryos that survive cryopreservation may be stronger than those that do not. Weaker embryos might be less likely to last an extended time in the lab and withstand the freeze-thaw process. It's a risk that you take when choosing frozen embryo transfer, but some doctors argue that the weaker embryos wouldn’t have led to a healthy pregnancy.

Older studies compared fresh vs. frozen transfer and concluded that fresh embryo transfer cycles had better pregnancy rates than frozen embryo transfers. However, that research cannot be applied to a “freeze-all” cycle.

The older research involved taking the less-than-ideal embryos, freezing them, and then immediately transferring the best-looking ones, It would be 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 kinds of FET-IVF cycles: hormonal support cycles and “natural” cycles. The most commonly performed FET-IVF cycle is a hormonally supported cycle, which is appealing to many people, clinics, and labs because the day of transfer is easy to control and hormonal support is available for any ovulatory problems.

If you want your primary doctor to perform the procedure and/or you want to have it done on a specific date, you need to be aware of what's actually possible with each FET-IVF type.

A synthetic cycle can be manipulated depending on the day of progesterone start, but with a natural cycle, it's up in the air.

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. You will receive injections of a drug meant to control and shut down the reproductive cycle—usually the GnRH agonist Lupron, but occasionally other pituitary-suppressing medications instead.

Once you get your period, your clinic will perform a baseline ultrasound and bloodwork. If all looks good, you will start estrogen supplementation. This is to help ensure a healthy endometrial lining. This continues for about two weeks, and then you'll have another ultrasound and more blood work.

After approximately two weeks of estrogen support, you will add another hormone: progesterone. You may need progesterone in oil injections or possibly vaginal suppositories.

The schedule for the embryo transfer is based on when progesterone supplementation started and at what stage the embryo was cryopreserved. For example, if the embryo was cryopreserved on day five post-egg-retrieval, then the frozen embryo transfer will happen six days after progesterone supplementation starts.

A benefit of a FET-IVF cycle is that requires significantly less monitoring than a conventional IVF cycle.

FET Natural Cycle

With a FET natural cycle, 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 with a hormone-supported cycle, that day will depend on whether the embryo was frozen on day three or day five post-egg retrieval.

Because the timing is essential, the cycle is closely monitored either at home, with ovulation predictor tests, or at the fertility clinic with ultrasounds and blood testing. 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, the clinic schedules your transfer date and you begin progesterone supplementation.

Some studies show an advantage to using a natural cycle over hormone-supported cycles. However, the research is still preliminary and inconclusive. "Despite the increase in FET, the most optimal priming protocol of the endometrium is still a matter of debate," noted the authors of a 2021 comprehensive review on this topic. The researchers also point out that it's very likely that there are individual differences that make one approach or the other more effective.

Risks

A frozen embryo transfer cycle has significantly fewer risks than a full IVF cycle. One of the primary risks of using IVF (and fertility drugs) is ovarian hyperstimulation syndrome (OHSS). However, OHSS is not a concern in a FET cycle because ovarian stimulating drugs are not used.

With cryopreservation, many embryos will survive the freeze and thaw process. If an embryo's PGT testing comes back as indeterminate (it's unclear whether it is normal or not) it can be re-biopsied. This lowers the success rate, but not significantly.

Embryo transfer has risks, including an increased risk of ectopic pregnancy and a very small risk of infection. Depending on how many embryos are transferred, the chance of multiple pregnancy may also be higher (which comes with its own set of risks for a pregnant person and the fetuses they are carrying).

Any time embryos are frozen, thawed and re-biopsied, and/or refrozen, there is a risk of losing them or lowering the success rate when it comes time to thaw for use. Still, that doesn't necessarily mean that fresh transfer is always the best answer.

Some research has indicated that there is some risk of babies from frozen embryo transfers being born large for gestational age. However, a meta-analysis found that both pregnancies and babies from frozen embryo transfers might be healthier than those from fresh embryo transfers. The researchers found that frozen embryo transfer babies were at lower risk for preterm birth, stillbirth, and low birth weight.

Another study compared the risks of a birth defect in fresh IVF transfers, frozen embryo transfers, and naturally conceived children. The study found that birth defects were three times more likely with fresh IVF transfers when compared to naturally conceived children. However, that increased risk wasn't seen with frozen embryo transfer (perhaps because these frozen embryos could have been tested with PGT). The overall risk of birth defects was still very low.

Costs

When talking to your doctor about the cost of FET, make sure the price they quote includes everything, as there may be a variety of fees associated with the treatment. This information will help you plan your budget accordingly. 

The average cost for a frozen embryo transfer is between $3,000 and $6,500.

The average price includes monitoring, hormonal support, and the costs associated with the transfer process itself. A natural cycle costs slightly less because it does not require fertility drugs. However, the expenses of the initial IVF treatment, as well as the initial cryopreservation of the embryos and any storage fees, are not included in the price.

A Word From Verywell

While you might assume that using fresh embryos for IVF would be inherently better than using frozen embryos, that's often not the case. Frozen embryo transfer is an effective option for many people using IVF, which is comparable or better than using fresh embryos. Whether or not FET is ideal in your circumstances depends on many individualized factors. Your doctor is the best source for information on whether or not this approach is the best choice for you.

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