Transfer of frozen embryos (FET)

Transfer of frozen embryos (FET)

If you have recently been treated for infertility or are considering IVF, you may be wondering what will happen to all the excess embryos that were created during the procedure.

If you and your partner have embryos that you did not use during the initial IVF procedure, these embryos can be frozen and then transferred to your uterus at a later date. Known as the "frozen embryo transfer (FET)", this procedure is now widely available in the United States and has helped many infertile couples get a pregnancy.


Frozen embryo transfer (FET) is a relatively new type of fertility treatment.

Introduced in the 1980s, this procedure takes the embryos that have been frozen for a period of time and put them back in your uterus after they have been thawed. FET is a relatively non-invasive procedure that many couples choose to do. It can be successfully performed on women who have a natural or controlled menstrual cycle.


Many couples choose to do a frozen embryo transfer (FET) if they have previously undergone an IUI procedure without success or if they have the remaining embryos from an initial IVF cycle. Some couples do not like the idea of ​​destroying the embryos just because they "remained" from an IVF cycle.

Other couples know or suspect that they will need a new IVF procedure in the future and prefer to freeze their embryos to make the next IVF cycle less psychically stressful for the woman. To make an IVF cycle, numerous embryos are created to ensure that healthy and viable embryos are sufficient for transfer.

Many couples decide to freeze some of these embryos to give them the opportunity to have a new pregnancy again in the future or to use them in an IVF cycle later. Couples receiving donated embryos must also undergo a FET frozen embryo transfer procedure, as all donated embryos must be frozen for at least 6 months to ensure their health and safety.

Freezing of embryos

The frozen embryo transfer (FET) procedure involves freezing or cryopreservation of your embryos. Embryos can be cryopreserved at different periods after fertilization, starting from day 1 to day 6 after fertilization. Cryopreservation of embryos allows your embryos to be kept healthy and viable for a period of up to 10 years. The freezing process takes place as follows:

  • your embryos are placed in vials of a special bottle, which is very similar to a drop
  • then the embryos are mixed with a special solution called cryoprotector; this cryoprotectant prevents the formation of ice between the cells of your embryos
  • The glass vials containing the embryos are then placed in a controllable freezer, filled with liquid nitrogen.
  • they are gradually cooled down to a temperature of -196 degrees Celsius.

Defrosting of embryos

Before the transfer of frozen FET embryos takes place, your embryos must be thawed after the freezing process. When the specialist decides it's time to start the FET procedure, your embryos will be removed from the freezer and thawed.

  • the embryos can freeze naturally, until they reach room temperature
  • the embryos are then passed through 4 different solutions, to help remove all traces of cryoprotective used during the freezing process
  • the embryos are then heated to body temperature (37 degrees Celsius) and mixed with a small amount of culture medium.

Transfer of frozen embryos

The transfer process of FET frozen embryos is currently quite easy to perform. It is very similar to the typical IVF embryo transfer procedure: your ovulation and endometrial development will be monitored and then the embryos will be placed in your uterus before the embryo transfer: before your embryos can be thawed and transferred you and the specialist doctor must decide together how many embryos will be transferred to your uterus.

The number of embryos transferred has a direct impact on the success rate of the frozen embryo transfer procedure (FET). Your doctor will monitor your body to determine when is the best time for embryo transfer. You will have numerous ultrasounds (probably 4 or 5) to monitor the follicular development in your ovaries and the thickness of the uterine mucosa.

The specialist doctor will try to associate the age of the embryos with the correct stage of the menstrual cycle. Typically, embryonic transfer occurs about two days after ovulation. The embryos will be thawed one day before the process of transfer of frozen embryos (FET).

Procedure: Currently, the transfer of frozen embryos is painless and easy, and lasts only about 15 minutes:

  • a catheter is inserted through the cervix to the uterus
  • embryos are injected into the catheter and stored in the uterus
  • It will ask you to stay still for several minutes, to allow the embryos to position themselves in the uterine mucosa.

After the transfer

After the transfer the specialist will probably want to continue the fertilization medication you have taken until then. 12 days after the frozen embryo transfer procedure (FET), you will return to the clinic for a pregnancy test.


The success rate of frozen embryo transfer (FET) depends on a number of factors, especially the age of the mother and the number of embryos transferred. Usually the success rate is around 20% per cycle. It is important to know that not all embryos will survive the freezing and thawing process they go through.

About 70% of embryos survive freezing and this can sometimes have an impact on the success rate of frozen embryo transfer (FET). This fact makes it necessary to freeze and thaw a sufficient number of embryos when performing the FET process.


The process of transferring frozen embryos (FETs) is quite expensive, although in some cases it is cheaper than the continuous IVF procedure. If fertilization drugs such as Clomid or Pergonal are used, the costs may increase per cycle.

Tags Embriotransfer Cryo-preserving embryos