The frozen embryo transfer (FET) is one of the crucial procedures of modern in vitro fertilization treatment. Unlike traditional embryo transfer, FET is characterized by freezing the most suitable embryo for later implantation in the uterus during the next ovarian cycle instead of transplanting it immediately after egg retrieval and fertilization.

FET allows fertility specialists to schedule embryo transfer for the most appropriate time during a woman’s menstrual cycle. It can be performed both after a failed IVF procedure, to give another chance to the remaining embryos, and as a separate treatment cycle, which is indicated when embryo transfer needs to be staged for any medical reason. If you are considering IVF treatment or have already had embryo freezing, then it is vital to understand the nuances of the frozen embryo transfer, its preparation, success rate, and schedule to have realistic expectations about the treatment.

What Is Frozen Embryo Transfer?

The frozen embryo transfer, also known as FET, refers to a procedure during which the thawed embryo is implanted into the uterus.

During the IVF cycle, the eggs are retrieved and fertilized in the laboratory. If the fertilization is successful, the embryos can either be transferred to the uterus during the same cycle or placed in the freezer, where they can be kept for an indefinite period of time.

In the latter case, the transfer can take place during the following cycle, after the lining of the uterus is prepared.

The protocol includes:

• Preparing the endometrium
• Endometrial monitoring
• Embryo selection and transfer
• Embryo thawing
• Embryo transfer to the uterus
• A pregnancy test is taken after the egg retrieval.

The exact protocol depends on the individual circumstances of each patient and should be determined by a fertility specialist.

Why Is Frozen Embryo Transfer Done?

There are several reasons why a fertility specialist may recommend FET instead of a fresh embryo transfer.

Additional embryos from an IVF cycle

More than one good embryo can occur during an IVF cycle.

Those extra embryos can be cryopreserved (frozen) for future use.

This allows patients to have another embryo transfer without having to go through the process of egg retrieval again.

Medical reasons for delaying transfer

Sometimes it’s best to wait to transfer an embryo rather than do it right away after egg retrieval.

Your fertility specialist may choose to freeze your embryos and transfer them in a later cycle if they feel the conditions in your body may not be optimal for an embryo transfer.

After a previous IVF cycle

FET can also be used if you’ve already gone through an IVF cycle, and you still have embryos frozen.

Embryo genetic testing

Sometimes embryos need to be tested prior to transfer. Testing can take some time, so embryos are frozen while waiting for results. A positive result can then be transferred in a later cycle.

Frozen Embryo Transfer Procedure: Step-by-Step

The frozen embryo transfer procedure is generally simpler than the egg-retrieval stage of IVF because no egg collection is required during the FET cycle.

Step 1: Initial Assessment

Your fertility doctor will go over your medical and reproductive history and assess if you are a good candidate for a frozen embryo transfer.

They may discuss:

• Menstrual cycle
• Uterine health and thickness of the endometrial lining
• Hormone levels
• Past IVF treatment
• Available frozen embryos
• Whether you’ve had a pregnancy or implantation before

They may also want to perform additional tests, depending on your individual situation.

Step 2: Preparing the Uterine Lining

The uterine lining needs to be suitable for embryo implantation, which means that a suitable endometrium must be present.

Depending on whether you have regular ovulations and your personal needs, there are two different treatment options for FET:

Natural or modified natural FET cycle:

If you have regular ovulations, your fertility team may try to estimate when you will ovulate and then try to time the embryo transfer to your natural cycle

Hormone replacement or programmed cycle:

Sometimes it is helpful to use hormone medication (estrogen and progesterone) to prepare the uterus and time embryo transfer.

The choice between these options depends on your personal circumstances and what your fertility doctor thinks would be best for you.

Step 3: Monitoring the Endometrium

During the preparation cycle, your doctor can use ultrasound and, if necessary, blood tests to monitor the condition of the uterine lining and hormone levels.

The aim is to establish when the uterus is ready for embryo transfer.

The timing and treatment requirements are individual for each patient

Step 4: embryo thawing

On the day of transfer, the thawed embryo chosen for transfer is carefully unfrozen by the embryology lab.

Embryos are typically frozen using a process called vitrification.

The embryology team evaluates the embryo after thawing before performing the transfer.

Step 5: embryo transfer

The embryo transfer is usually an outpatient procedure.

A thin, flexible catheter is inserted through the cervix into the uterine cavity, and embryos are placed inside the uterus.

The procedure is typically done without surgery or anesthesia.

You can go home after the transfer according to your doctor’s orders

Step 6: Pregnancy Test

Following embryo transfer you will be instructed to continue all prescribed medications and wait until the appropriate time to take a pregnancy test.

Testing too early can lead to a false negative.

Your fertility clinic will advise you when the appropriate time is to go in for your pregnancy blood test (typically a beta-hCG test)

How to Prepare for Frozen Embryo Transfer

Preparing for FET varies for each patient, but it is critical to follow your fertility specialist’s instructions closely.

Take the prescribed drugs according to the instructions

If fertility drugs, including estrogen, progesterone, or others are prescribed, they should be taken under the guidance of the doctor. Never stop taking the medications or change the dose without consulting your fertility team.

Visit the fertility clinic

The doctor may ask you to have an ultrasound scan and blood tests to check if the condition of the endometrium and hormone levels in your body are suitable for embryo transfer.

Maintain a healthy lifestyle

Having a healthy diet, getting enough rest, and exercising regularly is essential during the treatment. It is also necessary to quit smoking and limit alcohol consumption.

Check and treat existing disorders

Hormonal imbalance, thyroid diseases, diabetes, and other conditions must be treated before initiating the embryo transfer procedure.

Follow the fertility clinic’s guidelines

The fertility clinic might give you particular instructions regarding drugs, exercise, sexual activity, and other aspects of your daily routine and embryo transfer.

How Long Does Frozen Embryo Transfer Take?

The actual embryo transfer procedure is usually a quick procedure.

The entire FET process can take up several weeks, however, depending on the protocol used in your treatment.

This protocol can range from:

• the beginning of your menstrual cycle
• endometrial preparation
• ultrasound scans
• hormonal medication 
• thawing of the embryos
• embryo transfer
• pregnancy test

A natural-cycle FET will follow your natural ovulation while a programmed cycle will use medication to prepare your uterus for embryo implantation. Your fertility specialist will be able to advise you further on the expected length of your treatment based on the individual plan you will follow.

Frozen Embryo Transfer Success Rate

One of the most common questions patients ask is about the frozen embryo transfer success rate.

However, there is no general success rate that would apply to every FET cycle, since the pregnancy and live birth chances are affected by many variables:

• age at the time of the egg collection
• embryo quality
• embryo developmental stage
• chromosomal status 
• uterine and endometrial conditions
• the cause of infertility
• previous IVF history
• sperm and egg factors
• individual patient factors

Importantly, the age at the time of egg retrieval plays a critical role, especially when it comes to embryos made from the patient’s own eggs.

Patients should also differentiate between implantation rate, pregnancy rate and live-birth rate, since these are not the same.

When comparing clinics’ statistics, be sure to understand what percentage refers to which outcome and if the statistics were generated from patients that are comparable to you.

Is Frozen Embryo Transfer Better Than Fresh Embryo Transfer?

Neither option is inherently better for everyone.

Both fresh embryo transfer and frozen embryo transfer (FET) involve potential benefits and risks that should be evaluated by the patient and fertility doctor.

In a fresh embryo transfer, the embryo is placed into the uterus during the same IVF cycle as the egg retrieval.

During FET, the embryos are transferred during the following cycle after being frozen and thawed.

A fertility specialist may suggest FET if the situation calls for postponing embryo transfer or if the embryos have been frozen.

A fertility specialist determines which procedure is the best option based on factors related to the patient′s condition, rather than a simple comparison of success rates between the two procedures.

What Happens After Frozen Embryo Transfer?

After FET, the embryo must implant into the uterine lining and continue to grow.

Some patients report:

• Mild abdominal discomfort
• Bloating
• Breast tenderness
• Fatigue
• Mild spotting

These are not reliable signs of pregnancy, as these symptoms might also be caused by the hormones used during fertility treatment. At the same time, experiencing none of these symptoms does not necessarily mean that the treatment failed.

The most reliable way of knowing if the embryo transfer was successful is following the instructions of your fertility clinic regarding pregnancy testing.

What Should You Avoid After FET?

Your fertility clinic will give you specific directions to follow after embryo transfer.

In general, you should:

• Continue to take any medications prescribed
• Avoid smoking
• Ask your doctor if you should abstain from consuming alcohol
• Not take any new medications or supplements
• Come in for any follow-up visits that may be necessary

And contact your fertility clinic if you experience any concerning symptoms

Furthermore, in most cases, strict bed rest is not necessary simply because of an embryo transfer. Your fertility team can help advise you about how much activity is appropriate given your particular circumstances.

Frozen Embryo Transfer Risks and Considerations

FET is generally a safe procedure; however, as with all medical treatments, there are some risks and side effects.

These may include:

• That the embryo will not survive the thawing process
• Implantation failure
• Miscarriage
• Ectopic pregnancy
• Complications related to the infertility diagnosis or treatment

A fertility specialist can go over the risks and benefits of embryo thawing and transfer based on an individual’s circumstances and treatment plan.

What Happens If Frozen Embryo Transfer Is Unsuccessful?

An unsuccessful FET can be heartbreaking, but it doesn’t mean that further treatment attempts will be ineffective.

Your fertility doctor will go over the details of the failed cycle with you to understand what might have gone wrong. Some of the factors that they will consider include:

• Embryo quality and development
• Endometrial receptivity
• Uterine environment
• Hormonal balance
• Timing of embryo transfer
• And your history of previous fertility treatments

If there are more embryos available for transfer, another FET procedure can be considered. However, if no further embryos are available, your fertility doctor will talk to you about other possible treatment options.

Frozen Embryo Transfer vs Fresh Embryo Transfer

Your fertility specialist can determine which approach is appropriate based on your medical history and treatment goals.

Conclusion

Frozen embryo transfer (FET) is an increasingly important component of modern IVF treatment. It enables a previously frozen embryo to be transferred during a subsequent cycle after the uterus has been properly prepared.

The frozen embryo transfer procedure typically consists of preparing the endometrium followed by thawing of the selected embryo and its transfer into the uterus using a fine catheter.

Although FET can provide valuable benefits in many IVF treatment scenarios, its outcome is variable and depends on a range of patient-specific factors. Advanced maternal age, embryo quality, uterine receptivity and a range of other infertility-related variables can significantly impact the likelihood of pregnancy and live birth.

When considering FET, consult with a qualified fertility specialist to discuss your medical history, available embryos and treatment options. A personalized treatment strategy will help you understand the expected outcomes of the procedure and your individual chances of success.