Frozen Embryo Transfer (FET)
If you have recently gone through infertility treatments or if you are considering undertaking IVF, you may be wondering what will happen to any extra embryos that are created during the procedure. If you and your partner have extra embryos that are not used during initial IVF procedures, these embryos can be frozen and then transferred to your uterus at a later date. Known as frozen embryo transfer (FET), this procedure has helped many couples facing infertility achieve pregnancy.
What is Frozen Embryo Transfer?
This procedure takes embryos that have been frozen for a period of time and replaces them into your uterus after they have been thawed. FET is a relatively non-invasive procedure, which is why many couples choose to have it performed. It can be successfully performed on women who are experiencing either natural or controlled menstrual cycles.
Why Choose Frozen Embryo Transfer?
Many couples choose to have FET performed if they have had extra embryos remaining from an initial IVF cycle. Some couples do not like the idea of destroying embryos simply because they are "left over" from an IVF cycle. Other couples know or suspect that they will need to do IVF again in the future and prefer to freeze their embryos in order to make future IVF cycles less stressful physically for the female.
In order to perform IVF, numerous embryos are created in order to ensure that healthy and viable embryos are available for transfer. Many couples decide to freeze some of these embryos in order to allow them the opportunity to get pregnant again in the future or for use in a later IVF cycle.
Embryo Freezing
The FET procedure involves having your embryos frozen, or cryopreserved. The freezing procedure is as follows:
Your embryos are placed inside of special glass vials, that look much like straws.
These embryos are then mixed with a special solution, called cryoprotectant. This cryoprotectant prevents ice from forming in between the cells of your embryo. The glass vials containing the embryos are then inserted into a controlled freezer filled with liquid nitrogen.They are cooled slowly until they reach a final temperature of -196° C.
Embryo Thawing
Before FET can take place, your embryos must be thawed after the freezing process. When your reproductive endocrinologist decides it is time to begin the FET procedure, your embryos will be removed from the freezer and thawed.
The embryos are allowed to thaw naturally, until they come to room temperature.
The embryos are then steeped in four separate solutions to help remove any cryoprotectant used during the freezing process.
Your embryos are then warmed to body temperature (37°C) and mixed with a small amount of culture medium.
The Frozen Embryo Transfer Procedure
The FET procedure is actually fairly straightforward.
Before Embryo Transfer
Before your embryos can be thawed and transferred, you and your reproductive endocrinologist need to decide how many embryos to transfer into your uterus. The number of embryos transferred will directly impact the success rate of the FET procedure. Typically, between three and four embryos are transferred during each FET procedure.
Your health care provider will then monitor your body in order to determine the best time for the embryo transfer. We usually give oral estradiol tablets to prepare the uterine lining. The thickness is measured on ultrasound scan. Your embryos will be thawed the day before your FET procedure.
The Transfer
The actual transfer of the frozen embryos is painless and straightforward, and only takes about 15 minutes.
A catheter is inserted through your cervix and into your uterus.
The embryos are injected into the catheter and deposited in your uterus.
After the Transfer
After the transfer your reproductive endocrinologist will likely have you continue any fertility medications that you may be using. Twelve days after the FET procedure, you will return to your clinic for a pregnancy test.
Success Rates of Frozen Embryo Transfer
The success rates of FET really depends upon a variety of factors, particularly maternal age and the number of embryos transferred. Typical success rates are around 20% per cycle. It is important to know that not all embryos will survive the freezing and thawing process though. About 70% of embryos survive cryopreservation, and this can sometimes impact the success rates of FET. This makes it important to freeze and thaw a number of embryos when performing the FET procedure.
