If you’re undergoing in vitro fertilization (IVF), you may hear your fertility specialist recommend a frozen embryo transfer (FET) as part of your treatment plan. Rather than transferring an embryo shortly after egg retrieval, a frozen embryo transfer allows your care team to cryopreserve an embryo and transfer it during a later cycle.
Frozen embryo transfers have become an important part of modern fertility treatment. In 2022 alone, more than 184,000 assisted reproductive technology (ART) cycles reported to the CDC involved freezing all resulting eggs or embryos for future use.
But what is a frozen embryo transfer, and what should you expect if your fertility specialist recommends one? Below, we walk through the FET process, how it differs from a fresh embryo transfer, potential success rates, and why some patients may benefit from this approach.
What Is a Frozen Embryo Transfer?
A frozen embryo transfer, or FET, is a procedure in which a previously frozen embryo is thawed and transferred into the uterus with the goal of achieving pregnancy.
The process begins with IVF. During an IVF cycle, a fertility specialist retrieves eggs from the ovaries and an embryology laboratory fertilizes them with sperm. The resulting embryos develop in the laboratory before the care team determines which embryos are appropriate for transfer, cryopreservation, or additional testing.
Instead of transferring an embryo during the same cycle as the egg retrieval, the embryology team can freeze the embryo through a process known as cryopreservation. When the patient is ready for an FET, the laboratory thaws the selected embryo and the fertility specialist transfers it into the uterus.
This separation between egg retrieval and embryo transfer gives the fertility team more flexibility when planning treatment.
Frozen vs. Fresh Embryo Transfer: What’s the Difference?
The primary difference between a fresh and frozen embryo transfer is when the transfer occurs.
During a fresh embryo transfer, the embryo is transferred several days after egg retrieval, within the same treatment cycle.
With a frozen embryo transfer, the laboratory freezes the embryo after fertilization and development and the transfer then takes place during a later menstrual cycle.
That delay can offer several potential advantages. It allows hormone levels to return closer to baseline following ovarian stimulation and gives the fertility team additional time to prepare the uterine lining for transfer. An FET may also be necessary when patients choose preimplantation genetic testing (PGT), depending on the treatment plan and testing process.
However, frozen transfers are not always more successful than fresh transfers. Large randomized trials have found similar live birth rates between fresh and frozen embryo transfers. Your individual circumstances ultimately determine which approach makes the most sense.
The Frozen Embryo Transfer Process: What to Expect
Although every fertility treatment plan is different, the FET process generally includes several stages.
1. Preparing the Uterine Lining
Before transferring an embryo, your fertility team needs to make sure your uterine lining is ready for implantation.
Clinics can accomplish this through different FET protocols depending on factors such as your menstrual cycle, medical history, and previous treatment.
Some patients may undergo a natural or modified natural cycle, in which the fertility team monitors ovulation and coordinates the embryo transfer with the body’s natural hormonal changes.
Other patients undergo a medicated FET cycle. In these cycles, medications such as estrogen and progesterone help prepare the uterine lining and control the timing of the transfer.
Your fertility specialist will determine which protocol is appropriate for you.
2. Monitoring Before Your FET
Your care team will typically monitor your progress before scheduling the transfer. Depending on your treatment plan, monitoring may include ultrasounds and bloodwork to evaluate the uterine lining, hormone levels, and/or ovulation.
These appointments help your fertility specialist determine the optimal timing for embryo transfer.
3. Thawing the Embryo
Before the procedure, the embryology laboratory carefully warms the embryo that’s going to be transferred.
Modern embryo cryopreservation commonly uses vitrification, a rapid-freezing technique designed to minimize damaging ice-crystal formation. Your embryology team evaluates the embryo as part of the thawing process before proceeding with transfer.
4. Transferring the Embryo
The embryo transfer itself is generally a relatively quick procedure and doesn’t require egg retrieval or surgery.
During the procedure, the fertility specialist places a thin catheter through the cervix and into the uterus. The embryo travels through the catheter and into the uterine cavity, typically using ultrasound to guide it
Many patients experience little or no discomfort, although some may notice mild cramping or pressure.
Afterward, your fertility team will provide instructions regarding medications and activity.
5. Waiting for Your Pregnancy Test
Then comes one of the most anticipated parts of fertility treatment: waiting to find out whether the implantation stuck.
Your clinic will schedule a blood pregnancy test after the transfer to measure human chorionic gonadotropin (hCG) and your exact timing depends on your clinic’s protocol and the developmental stage of the embryo.
It can be tempting to take an at-home pregnancy test earlier, but testing too soon may produce an unclear or inaccurate result, so it’s important to follow the testing schedule provided by your fertility team.
What Happens After a Frozen Embryo Transfer?
Most patients can return to many of their normal daily activities shortly after an embryo transfer unless their fertility specialist recommends otherwise.
If your FET involves hormone medications, you may also need to continue progesterone and/or estrogen after the procedure. Don’t stop prescribed fertility medications because of symptoms (or lack of) or the results of a home pregnancy test unless your fertility care team tells you to do so.
You may experience mild symptoms such as cramping, spotting, bloating or breast tenderness. However, you can’t tell from these symptoms alone whether an embryo has implanted. Fertility medications can produce many of the same sensations associated with early pregnancy.
Your scheduled blood test provides a much more reliable answer.
Who May Benefit From a Frozen Embryo Transfer?
There is no single embryo transfer strategy that works best for every IVF patient. Fertility specialists recommend FET based on each patient’s medical history, ovarian response, embryo development and overall treatment plan.
A frozen embryo transfer may be particularly useful for patients who:
- Have embryos remaining from a previous IVF cycle
- Plan to undergo certain types of preimplantation genetic testing
- Need or want to postpone pregnancy after embryo creation
- Have a medical reason to delay embryo transfer
- Develop a high ovarian response during IVF stimulation
- Face an increased risk of ovarian hyperstimulation syndrome (OHSS)
- Are pursuing another pregnancy using embryos frozen during an earlier IVF cycle
How Successful Are Frozen Embryo Transfers?
Research has shown that frozen embryo transfers can achieve live birth rates comparable to fresh transfers for many patients.
In a large randomized trial involving more than 2,100 ovulatory women undergoing IVF, researchers found no significant difference in live birth rates between frozen and fresh embryo transfer groups: 48.7% compared with 50.2%, respectively.
However, outcomes can differ for specific patient populations. For example, a randomized study involving patients with polycystic ovary syndrome (PCOS) found higher live birth rates after frozen embryo transfer than after fresh transfer in the population studied.
It’s important to remember that IVF success can vary based on several factors, including:
- Age
- Infertility diagnosis
- Previous pregnancy history
- Previous ART treatment
- Whether patients use their own or donor eggs
- The specific ART procedures used
For this reason, you can’t predict your personal likelihood of pregnancy based on a national average or another patient’s experience. The CDC specifically cautions patients that published clinic success rates don’t represent any one patient’s individual chance of success.
Is a Frozen Embryo Transfer Right for You?
A frozen embryo transfer gives fertility specialists flexibility to separate embryo creation from the timing of pregnancy. For some patients, FET allows time for genetic testing, reduces risks associated with a high ovarian response, or makes it possible to return for another pregnancy using embryos created years earlier.
For others, a fresh embryo transfer might be a better option
At Red Rock Fertility Center, we create personalized fertility treatment plans based on your medical history, fertility testing, treatment goals, and individual response to IVF. Our team can help you understand whether a fresh or frozen embryo transfer may be right for you.
If you’re considering IVF or have questions about FET, schedule a consultation to learn more about your treatment options.
