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A frozen embryo transfer ( FET ) is a cycle in which the remaining frozen embryos from a previous fresh IVF/ICSI or donor oocyte cycle are thawed and then put back or transferred into the woman's uterus.

The chance of having embryos available to freeze greatly depends on age. The success rates of an FET cycle are comparable to fresh IVF cycles—and sometimes result in an higher success rate because of the opportunity to optimize the lining of the uterus before implantation, among other reasons. Both fresh and frozen cycles have the same primary indicator for success: the maternal age at the time of embryo freezing. Frozen embryos remain viable for an infinite amount of time after the initial freeze. You may choose to do an FET cycle following an unsuccessful fresh IVF cycle or after a successful fresh IVF cycle if you’re ready to expand your family.


Frozen embryo transfer success rates - what are the chances of frozen embryo transfer working?

This depends on several variables

    • Age of the woman

    • Quality of the frozen embryos

    • Stage of the frozen embryos (day they were frozen, day 3 or day 5-6)

    • The quality of the uterus and how it is prepared for the FET

    • The IVF lab's embryo freezing protocol and their expertise with cryopreservation of embryos

A healthy human embryo will hatch from its shell on day 5-7 after fertilization and implant within hours after hatching out. So actual invasion of the embryo with attachment to the uterine wall occurs about 2-5 days after a day 3 transfer and within 1-3 days after a day 5 transfer.


What is the purpose of freezing spare embryos?

  1. Transfer of frozen thawed embryos from your previous IVF cycle gives you another chance at achieving a pregnancy without undergoing a full IVF cycle.

  2. Embryos from an IVF cycle where a transfer is medically not appropriate can be frozen so that the clinical problems can be rectified before embryos are transferred. example:

  • Patients at risk of Severe Ovarian Hyperstimulation Syndrome

  • Inability to transfer embryos because of obstruction or another abnormality in the cervix

  • Patients undergoing this treatment prior to treatment for cancer so that they can store fertility

The embryos are transferred back to the womb after suitable preparation of the lining of the womb. As the embryos already exist, this cycle does not involve stimulation of your ovaries or an egg collection.


Embryo freezing:


  1. At the time of embryo transfer, your clinician will discuss the fertilisation, growth rate and grade of embryos , day 3 or 5-6 which is based on the embryo's appearance and will offer embryo freezing when deemed appropriate. Approximately 60% of embryos judged suitable for freezing survive and embryos with lower grades would have an even lower chance of survival and so are mostly decided by the embryologist not to freeze. 

  2. Embryo freezing can only performed with your prior written consent. The legal storage limit for embryos is a maximum of 5 years from the date of freezing and this can be extended to 10 years if in the interim the female partner has reached the peri-menopausal years.

  3. The embryos are your property and responsibility. You also have to decide the fate of the embryos in the event of death or mental incapacitation. They deserve similar considerations as those for your unborn future child. Therefore we strongly advise you to always remain in touch with your fertility expert or clinic to advise them of your change in address, intentions and suggest that you consider replacement of your frozen embryos at the earliest possible date. 

Embryo donation:

  1. You can consider donating your embryos to help another couple. This is very similar to egg and sperm donation, you would be required to have implication counselling and the necessary screening tests.

  2. Your clinician will advise you to consider this option for your frozen embryos after you have completed your family or decided to discontinue all future treatment for yourself.

Long term storage:

This section is primarily for those couples who wish to do the storage of embryos prior to chemo or radiotherapy for cancer.

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