Guide to Frozen Embryo Transfers (FET)

For those of you exploring fertility treatment options, you’ve no doubt come across a wealth of information about in vitro fertilization (IVF). But did you know that there are two methods of IVF treatment? With a fresh embryo transfer, one or more fertilized eggs will be implanted into the uterus three to five days after egg retrieval. Below, you will find everything you need to know about the second method, frozen embryo transfer (FET), which can take place months, or even years, after your initial egg-retrieval procedure. 

What is in vitro fertilization? 

In vitro fertilization (IVF) is a popular form of assisted reproductive technology (ART) that involves retrieving eggs, fertilizing them in a lab setting to create embryos, and then transferring the embryos into the uterus where they will hopefully implant and result in pregnancy. 

The process begins with a course of injectable ovary-stimulating medications to help you produce multiple eggs in one menstrual cycle. These medications are taken for 8 to 12 days, with blood work and ultrasounds performed to monitor their effect and your body’s response to them. 

Once the eggs are mature, there is an outpatient surgical procedure to retrieve them. At this point, the male partner or donor provides a semen sample, which will be combined with the retrieved eggs in the lab. The resulting fertilized eggs will be monitored by an embryologist for up to five days.  

Typically, the developed embryos are then transferred into the uterus. However, the embryos can be effectively frozen for future use if you aren’t yet ready to have children, or if your doctor recommends that you wait until your body is better prepared, hormonally. 

What is a frozen embryo transfer (FET)? 

Similar to the standard IVF treatment cycle, a frozen embryo transfer is a process whereby an embryo or embryos that have been fertilized and developed in a lab are transferred into your uterus during your window of implantation (WOI). With FET, the embryo transfer doesn’t happen within three to five days following your egg retrieval. Instead, your embryos will be cryopreserved to later be thawed in time for your transfer procedure. 

The transfer process is identical to that of a fresh embryo transfer. During the procedure, you may be given a mild sedative. Your fertility specialist will insert a long, thin catheter into your vagina, through your cervix, and into your uterus. They will then use a syringe containing your embryo or embryos suspended in a small amount of liquid to place them into your uterus. Embryo implantation typically occurs within five days of this procedure. 

How is a frozen embryo transfer different from a fresh embryo transfer? 

Unlike a fresh embryo transfer, you will not have to go through ovarian stimulation and egg retrieval as part of the transfer process. More specifically, you won’t need to take the fertility medication to induce the production of multiple eggs during a single menstrual cycle. Nor will you have to undergo the surgical procedure to retrieve those eggs in the days before your transfer, because this will have already been completed earlier in your IVF journey. 

This means that all of the focus will be on growing and preparing your uterine lining for the embryo implantation process. 

The frozen embryo transfer timeline 

The embryo transfer itself is a relatively short in-patient procedure, but there are two to three weeks of treatment leading up to the procedure. Your timeline will likely look something like the following: 

Cycle Day	What to Expect
Day 2 or 3	You will have an appointment for baseline ultrasound and bloodwork. This baseline will be used to assess how you are responding to hormone medication. After your baseline, you’ll begin your medication regimen.
Days 3 to 14	You will continue taking estrogen as prescribed by your fertility specialist.
Day 14 or 15	You will return to your clinic for an ultrasound to check the thickness of your endometrium. If it is at least 7 mm thick, you’ll start taking progesterone. If your endometrium isn’t ready, you will return for another ultrasound after a few more days of estrogen.
Day 20 or 21	Your embryo(s) will be thawed, and you’ll be scheduled for your transfer procedure.

The final step of the FET timeline is pregnancy testing, which will occur two weeks after your transfer procedure. Often referred to as the Two-Week Wait or 2WW, the delay is necessary because it takes about two weeks for pregnancy hormone levels to stabilize enough to be consistently detectable in your bloodwork. While tempting, testing before then often returns false results. 

Reasons to opt for a frozen embryo transfer 

Frozen embryo transfers provide prospective parents with more options while undergoing IVF treatment. There are many different reasons that fertility specialists may recommend FET. Ultimately, this is a decision you will make with your doctor, but below you’ll find some of the common reasons to opt for FET-IVF. 

You have extra embryos after your fresh embryo transfer 

Whether you opted for a single or multiple embryo transfer, it is not uncommon to have more embryos than you need for a single IVF treatment cycle. Cryopreservation technology gives you the option to freeze these embryos to use them at a later date. 

You’ve decided to have another child through IVF 

As mentioned previously, any unused viable embryos from a previous IVF treatment cycle can be stored and used years later if you decide you want to have more kids. 

You’ve chosen to do preimplantation genetic testing (PGT) 

Since your embryos are fertilized and matured in a lab setting, the additional time afforded by a FET allows for the possibility of performing genetic screening. While this is an elective service, it can grant you peace of mind about any genetic conditions that may be in your family history or if you’ve reached an age when aneuploidy is more likely to occur. 

You need extra support creating the ideal uterine conditions for implantation 

There is a theory that the medications used to stimulate the ovaries may make it harder to create the ideal uterine environment for embryo implantation. For women who struggle with achieving adequate endometrial thickness, specialists commonly recommend waiting one or two months for the drugs to pass out of their system and to give their body a chance to rest before attempting a transfer. 

You’re at high risk for OHSS 

Ovarian hyperstimulation syndrome (OHSS) is a condition resulting from the fertility medications used to stimulate the ovaries. This is a relatively uncommon condition, but it can cause a lot of discomfort. Unfortunately, the symptoms of OHSS only resolve when you get your period, making it a common reason fresh embryo transfers are canceled. 

Your fresh embryo transfer was canceled 

As stated above, it is possible that your fresh embryo transfer could be canceled. There are many potential reasons: if you catch a cold or flu between your egg retrieval and transfer date, or your uterine lining isn’t quite ready, for example. In these situations, your fertility specialist may recommend cryopreserving all of your embryos and scheduling a cycle of FET-IVF at a later date. 

You’re using donor embryos 

Parents with unused embryos that they decide they won’t need can donate them. This allows same-sex couples and parents who are otherwise unable to produce their own embryos to still have children. If you use donated embryos, it is unlikely that you will be able to do a fresh embryo transfer. 

You froze your eggs when you were younger 

If you have already been through the egg-freezing process, either as fertility preservation before undergoing medical treatment that could impact your reproductive health, or simply because you wished to ensure you’d be able to get pregnant in the future, your IVF treatment will require a frozen embryo transfer. 

What are the benefits to choosing a frozen embryo transfer? 

The main benefit of FET is that you have a lot more freedom to choose when to undergo the embryo transfer. When you opt for a fresh embryo transfer, the procedure must occur within a few days of the egg retrieval because embryos that have developed past the blastocyst stage are no longer viable for implantation and your endometrium will reject them. Cryopreservation stops development in its tracks, allowing you as much time as you need before you’re ready to attempt the embryo-transfer process. 

Why would you want to wait to transfer your embryos? One reason might be to allow you to focus on creating the ideal uterine conditions for implantation. It’s not uncommon for women to need a bit of help ensuring their endometrium develops to an adequate thickness to support implantation. 

There may be other reasons to delay the process. For example, you might develop OHSS symptoms during the egg-retrieval stage, or you might experience high levels of stress that could significantly impact IVF success rates. 

Medicated versus unmedicated frozen embryo transfer 

Another benefit of frozen embryo transfers is that it is possible to undergo the procedure without taking any medication at all. This is referred to as a natural frozen embryo transfer cycle. Some women may not need assistance to ensure adequate endometrial thickness, while others may choose to undergo IVF treatment for reasons other than female-factor or unexplained infertility. In these cases, they can forego hormone medication altogether. 

Similarly, those who do opt for hormone support may be able to take oral hormone medication, rather than the injectable hormones that are necessary for egg retrieval. 

Are there any risks to undergoing a frozen embryo transfer? 

As with any medical procedure, there are some standard risks with FET, but the chances of negative outcomes are relatively low. Hormone medication may cause side-effects, but these are fairly mild and can be managed at home with over-the-counter medications like ibuprofen. If you have ever taken oral contraceptives, you’ve probably already experienced some of these side-effects. 

Otherwise, there is a minimal risk of infection, as well as complications related to anesthesia if you opt for sedation. Your doctor will walk you through these risks and how they can be managed before you have your procedure. Some women may also experience a change in vaginal discharge or cramping in the days after their procedure. 

How do you prepare for a frozen embryo transfer? 

In vitro fertilization is a lengthy process that involves a number of doctor’s appointments, medications, and lab work regardless of the type of embryo transfer you undergo. However, there are many things that can help you manage all of the ups and downs of fertility treatment. Maintaining a healthy diet and following a moderate exercise routine can help ensure your body has everything it needs during treatment. Additionally, having a strong support network in place, as well as practicing self-care and self-compassion, can help maintain your mental health during treatment.