Frozen Embryo Transfer (FET) is a fertility procedure where a previously frozen embryo is thawed and transferred into the uterus to attempt pregnancy. FET is performed after embryos are created and frozen during IVF. The uterus is prepared either naturally or with medications, and embryo transfer is timed to improve implantation chances.
Frozen Embryo Transfer (FET) is an important part of modern fertility treatment and is commonly used after IVF treatment. It involves transferring an embryo that was previously frozen during an IVF cycle into the uterus in a separate cycle.
Many couples choose or are advised to use FET because it offers flexibility, supports better uterine preparation, and allows the body to recover after ovarian stimulation. FET is now a standard and widely used fertility treatment option for couples planning pregnancy through IVF.
This page explains what FET is, how it works, who it is recommended for, the procedure step-by-step, timeline, success factors, and how it compares to a fresh embryo transfer.
A frozen embryo transfer (FET) happens when an embryo, created and frozen during an earlier IVF cycle, is thawed and then placed into a woman’s uterus. This gives couples a chance to use embryos saved from previous treatments, increasing their chances of getting pregnant without going through another full IVF process.
Frozen Embryo Transfer is a procedure in which:
FET is performed after embryos are created during IVF and stored through embryo freezing.
Before the transfer, the woman may need to take some medications to prepare her body. These medications help make her uterus ready to receive the embryo. After the embryo is transferred into the uterus, there’s a period of waiting to see if it successfully implants and leads to pregnancy.
FET is especially helpful when there are extra embryos from a past IVF treatment or when a couple wants to freeze their embryos for future use. It’s a common and reliable part of fertility treatment, providing flexibility and more opportunities for hopeful parents to start or grow their family.
FET is commonly recommended for:
FET allows embryo transfer in a cycle that is medically optimized for implantation.
Utilization of Remaining Embryos: If you have extra embryos from a past IVF cycle, a frozen embryo transfer (FET) allows you to use them without starting a new IVF cycle.
Medical Considerations: If you face complications like ovarian hyperstimulation syndrome (OHSS), which can make a fresh transfer risky, an FET is a safer option. It allows you to delay the transfer until the conditions are better.
Timing and Scheduling Flexibility: FET gives you the flexibility to schedule the embryo transfer at a time that works best for you, making it easier to plan around personal or work commitments.
Optimizing Uterine Conditions: If your uterine lining isn’t ideal during a fresh cycle, FET lets you take extra time to improve it, which can increase the chances of successful implantation.
Preimplantation Genetic Testing (PGT): For embryos that have been genetically tested, FET allows you to use them later, potentially increasing the likelihood of a successful pregnancy by selecting embryos with fewer genetic risks.
Addressing Previous Transfer Failures: If previous fresh embryo transfers haven’t worked, FET might offer better success rates, as it allows for improved uterine conditions and better preparation.
Doctors assess:
The uterus can be prepared using:
Doctors recommend the best approach based on cycle regularity, hormone levels, and medical needs.
Monitoring may include:
Monitoring helps ensure ideal timing and uterine readiness.
The frozen embryo is thawed carefully in the lab. Embryologists assess survival and readiness for transfer.
The embryo is transferred into the uterus using a thin catheter. This procedure is usually painless and does not require anesthesia.
A pregnancy test is done after the recommended waiting period to confirm whether implantation has occurred.
The timeline depends on whether the cycle is natural or medicated.
In general:
The actual embryo transfer procedure takes only a few minutes.
FET and fresh embryo transfer both aim to achieve pregnancy, but they differ in timing.
Doctors choose between FET and fresh transfer based on safety and medical factors.
FET success depends on:
Embryo quality and development stage influence implantation potential.
A healthy uterine lining supports implantation.
Even though embryos are frozen, age at the time eggs were retrieved affects embryo quality.
Accurate progesterone timing and proper uterine preparation play a key role.
Conditions such as endometriosis, fibroids, or thyroid issues may impact implantation.
FET offers several advantages:
Frozen embryo transfer is widely used and generally considered safe. However:
Doctors minimize risks through personalized planning and monitoring.
Success rate of frozen embryo transfer differs under various age categories .For women under the age of 35, the success rate of Frozen Embryo Transfer (FET) is between 40-60% per transfer. As women get older, the chances of success usually decrease. For women over 40, success rates for fertility treatments are typically between 20% and 30%. These rates can differ based on the quality of the embryos and the methods used by the fertility clinic.
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We usually expect a minimum of 8 mm thickness before replacing the embryos.
The lining may be unsatisfactory in one month and pick up in other months or with different methods of endometrial preparation as discussed before. In few women with persistently thin endometrium, we may have to rule out few causes like;
Endometritis due to an active infection.
Damage of lining due to previous genital tuberculosis.
Damage of lining due to previous trauma or surgery.
The endometrial lining in an ongoing IVF cycle may be suboptimal due to a state of increased estrogen production and hence where there are multiple follicles developing, we prefer to freeze all the embryos and replace them at a later date.
Also, in such patients, we have the very important advantage of avoiding OHSS when we give an agonist trigger, freeze all and plan FET at a later date.
When the endometrial lining is more than 14-15 mm, the pregnancy rates may decrease and hence it is better to postpone transfer and rule out any pathology in the uterus like
Presence of endometrial polyps.
Presence of submucosal fibroids.
Endometrial hyperplasia.
Incomplete shedding of the endometrium.
A minimum of 8 days of oestrogen intake is advisable for adequate endometrial preparation. Though maximum duration has been reported upto even 40-60 days, usually we give for a period of 15-25 days before deciding to transfer or cancel the cycle.
Usually, the frozen embryo is thawed on the same day as the transfer. Thawing it the night before might cause it to develop differently than the lining of your uterus. It’s important to follow all instructions carefully, including giving consent and deciding how many embryos to thaw, to ensure everything goes smoothly.
Embryos can be frozen for a long time without losing their quality. They’re just as good as when they were first frozen, so you can use them later with the same chance of success. This makes it easy to save embryos for the future without worrying that they’ll deteriorate.
After the transfer, rest for at least a day, then you can return to your usual activities, but continue taking any prescribed medications, like progesterone.
You’ll wait about 12 to 14 days to see if you’re pregnant, and consult your doctor for the results and further steps .
After the wait, you’ll see your doctor to discuss the results and next steps
