Frozen Embryo Transfer (FET) is a form of IVF that uses embryos that have been created during a previous cycle of treatment, and deep frozen for later use.

Embryos are placed in a special solution to protect them from damage and stored in liquid nitrogen at around minus 190 degrees centigrade.

When required, they are simply thawed out and implanted in the same way as a standard IVF embryo.

This article on frozen embryo transfer (FET) is written by Jackie Griffiths, a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites. 

Who can benefit from it?

FET can be of huge benefit to couples undergoing IVF, as it means that if their first cycle is unsuccessful they’re able to try again much more easily. Having a frozen embryo eliminates the need for egg or sperm collection and can reduce the amount of hormone stimulants required. It also avoids the risks of Ovarian Hyper-stimulation Syndrome (OHSS). What’s more, using frozen embryos can significantly cut the cost of a treatment cycle (although there will be some costs involved in storage).

FET is also of huge benefit to women who are facing an infertile future as a result of surgery, chemotherapy, or disease. As long as a healthy uterus remains, FET could still allow a successful pregnancy.

Occasionally, FET is recommended for women undergoing IVF if there is a high risk of severe OHSS, as the hormones produced in pregnancy can make this worse. In this case, the embryos are frozen to allow the woman to recover from the stimulation phrase before they’re implanted.

The process 

Embryos can be frozen at several stages of development:

  • Pronuclear Stage – embryos can be frozen immediately after fertilisation, giving them the highest chance of survival. However, as the embryos have not developed at this stage, it is hard to assess their viability.

  • Cleavage stage – embryos can be frozen at the first division stage, two or three days after fertilisation, allowing for limited assessment.

  • Blastocyst stage – embryos are most often frozen at the 8+ cell stage, the same point at which they would normally be transferred to the uterus - when the healthiest embryos can be easily identified.

Embryos are usually frozen for a maximum of five years, although this can be extended to ten. In the case of cancer patients, this limit may be extended further.

In order to create the ideal conditions for successful conception, the woman’s cycle is usually chemically controlled. This ensures the uterus has thickened properly and is ready to accept the embryo on the appointed day. A series of hormone treatments is prescribed, starting with oestrogen to thicken the lining of the uterus, followed by progesterone to mature the uterus ready for implantation.

Because the embryos can be thawed when needed the process is far more flexible than standard IVF, which is governed by follicle growth, and so puts less pressure on the woman involved.

It is possible to undergo frozen embryo transfer as part of a normal menstrual cycle, but the natural variation of this can create planning problems for both the patient and the clinic.

As a rule, no more than two embryos are implanted, however, in the case of women over forty, a third embryo may be considered.

Success Rates and Risks 

While the average survival rate for frozen embryos is around 60%, there is a chance that none will survive, and couples should prepare themselves for this possibility.  Furthermore, the success rate for conception using frozen embryos is generally lower than when using fresh embryos, although this is improving as the technology advances.

While there is no risk from OHSS when using frozen embryos, the other risks associated with IVF treatment remain, including an increased chance of ectopic pregnancy, and the problems of multiple births.

Legal Issues  

  • Embryos cannot be frozen without the informed consent of both parties.
  • Embryos cannot be used after the male partner’s death without prior consent.
  • The late father’s name cannot be added to the child’s birth certificate without prior consent.
  • The fate of the embryos in the event of the mother’s death should also be agreed in writing.


As previously noted, because the process is far simpler the cost of private FET treatment is considerably less than the cost of standard of IVF, at around £1,000 per cycle. The cost of freezing and storing the frozen embryos is between £200 and £300 per year.

As with standard IVF, the availability of NHS treatment will vary between health authorities and should be checked locally.

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