Frozen embryo transfer (FET)

Embryo freezing

After a cycle of IVF or ICSI, you may have leftover embryos that have been frozen. This procedure allows you to use these embryos at a later date – rather than having another IVF cycle.

Embryos may also be frozen for other reasons, such as due to social or medical reasons (whereby embryos may have been frozen rather than transferred as part of a fresh cycle).

When the embryos are ready to be used, they will need to be thawed before they are transferred into the patient’s uterus. Across the UK, around 90% of embryos survive the thawing process.

What is the process?

Treatment for those that have embryos in storage ready for use.

Drug stimulation

Your treating doctor will set up a treatment plan. This will include information and drug dosages required to prepare for you for the transfer.

The fertility medication will be used to thicken the lining of the womb, getting you ready for embryo implantation.


Once your uterus is ready, the thawing process begins.

Your embryos are removed from liquid nitrogen.

Only one or two may be removed and thawed, depending on how many you have frozen.

Your embryologist will examine your thawed embryo under the microscope and confirm it is suitable for transfer.

You will then be required to go to your chosen partner clinic for transfer.

Embryo transfer

During the embryo transfer, a thin tube will be passed through your cervix.

Through the tube, the embryo(s) will be transferred with a small amount of fluid.

The number of embryos transferred will depend on your treating doctor / clinic – usually 1 or 2. This reduces the risk of multiple pregnancies.

Monitoring / pregnancy test

After embryo transfer, you will continue taking hormone medications to support embryo implantation and early pregnancy (unless you had a natural cycle transfer, in which case no medication is required).

After around 9-12 days after the embryo transfer, a pregnancy test (Beta HCG blood test) can be conducted.

If the test is positive, you will continue to take the medication and start with pregnancy scans to monitor the growth of the embryo.

If the test is negative, you will stop taking the medication and wait for your period to start.

Success rates

According to the HFEA, success rates for IVF using frozen embryos have been increasing year-on-year, and are now comparable to rates using fresh embryos.

National birth rate per embryo transferred using woman’s own eggs and partner sperm, 2017:

  • under 35: 27% frozen, 30% fresh
  • 35 – 37: 26% frozen, 23% fresh
  • 38 – 39: 21% frozen, 15% fresh
  • 40 – 42: 15% frozen, 9% fresh
  • 43 – 44: 8% frozen, 3% fresh
  • Over 44: 4% frozen, 2% fresh

Further information can be found on the HFEA website.

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