Frozen Embryo Transfer (FET) Procedure

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A frozen embryo transfer (FET) is a type of IVF treatment where a cryopreserved embryo created in a full IVF cycle is thawed and transferred to a uterus.

FET typically uses “extra” embryos a couple has from a previous conventional IVF cycle. A cryopreserved embryo can also be a donor embryo.

There are many possibilities with donor embryos, including full embryo donation, the donation of an egg that can be inseminated with a partner's sperm, or the donation of sperm that can be inseminated into a partner's egg.

A "fresh" embryo isn't necessarily preferred, but it can be helpful in some cases. For example, in younger patients when there is not suspected chromosomal issue or in older patients who have embryos that didn't make it to testing in the lab that might have a better chance in utero without testing.

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.

Why Choose Frozen Embryo Transfer?

If you have certain health conditions or circumstances, you might want to consider 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. You may have cryopreserved embryos after a fresh IVF transfer fails.

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.

You might choose to freeze or cryopreserve any "extra" embryos after your IVF cycle.

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 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.

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.

Your could also choose to do another fresh cycle and not use your cryopreserved embryos, though this is a more expensive option.

You're Using Genetic Screening

FET is often part of preimplantation genetic testing (PGT). You might be able to do FET using untested, "leftover" embryos from PGT. You might have embryos to use because you froze them all to begin with for the testing.

Preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS) are assisted reproductive technologies that screen embryos for specific genetic disease or defects. This is done through a biopsy 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, all embryos that were biopsied will be cryopreserved.

Once the results come back, your doctor can decide which embryos to transfer for your FET-IVF cycles.

You Choose an Elective Procedure

You might choose elective frozen embryo transfer with or without PGD/PGS. With the “freeze all” protocol, the fresh embryo transfer isn’t part of the plan. This can occur with PGD/PGS or without genetic screening.

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. In turn, this could mean that a fresh transfer might be less likely to result in a viable, healthy pregnancy.

To avoid this outcome, 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.

Fresh Embryo Transfer 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.

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?

Studies have found that pregnancy rates are 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, which means it's unclear what people over age 35 or with a poor prognosis could expect.

More high-quality research needs to be done 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.

One 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) might be better for implantation.

The second possibility might be that the embryos that survive cryopreservation are stronger than those that do not. Weaker embryos might be less likely to survive an extended time in the lab and 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 couples, 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. 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 might 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, and then another ultrasound and more blood work will be ordered.

The monitoring during a FET-IVF cycle is significantly less than it is during a conventional IVF cycle.

After approximately two weeks of estrogen support, progesterone support is added. This can occur via progesterone in oil injections or possibly with vaginal suppositories.

The embryo transfer is scheduled based on when progesterone supplementation was started and on 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.

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.

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, you don't need to worry about OHSS in a FET cycle because ovarian stimulating drugs are not used.

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).

With cryopreservation, many embryos will survive the freeze and thaw process. If the embryo 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.

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 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 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 (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. This information will help you plan your budget accordingly. 

The average cost for a frozen embryo transfer is between $3,000 and 5,000.

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.

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