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Frozen Embryo Transfer (FET)

What is it?

Cryopreservation of embryos (freezing) is performed on all embryos not used in the ‘fresh’ cycle of IVF or ICSI. These have shown no increase of abnormalities in children born from frozen embryos, than those from ‘fresh’ embryos. Embryos can be frozen after 24, 48 or 72 hours in culture and also at blastocyst stage. Consent forms are signed relating to the “ownership” of the embryos in the event of death/divorce etc and any disputes are directed to the Commissioner of Health.​​


Why is it used?

Usually more then one embryo is created from an IVF/ICSI cycle. Those that are not used in the IVF/ICSI cycle are then frozen for later used in a FET (frozen embryo transfer) cycle.

How is it done and how will I feel?

Your specialist gynaecologist will organise a cycle plan for your FET cycle at Fertility North. The specialist may require you to have an appointment with them to discuss this plan prior to commencing your treatment cycle. You will also need to make a booking for an FET cycle, so please check with the Nurse Coordinator in advance. Please telephone Fertility North approximately a fortnight before your cycle to arrange a time to sign consent forms, as we will not thaw any of your embryos without your written consent. One of these consents must be signed for each transfer cycle. It is also necessary for you to pay the appropriate pre-payment before you begin your FET cycle.

The frozen embryo transfer cycle is relatively non-invasive compared to an egg collection cycle. The embryos can be replaced either in a natural cycle or in a controlled medicated cycle. We aim to transfer the embryos into your uterus at the correct time in relation to ovulation and the thickness of the lining of your uterus (endometrium). Often this is done by using ovulatory medication to better time the transfer.

In a “natural” FET cycle (where no medications are used before the embryo transfer), the cycle is tracked for ovulation using blood tests to monitor the hormone levels. As ovulation draws near an ultrasound will be requested to measure the thickness and maturity of the endometrium. If this is suitable, the embryo transfer will be performed 2-3 days after ovulation.

​​In a “controlled” FET cycle, Progynova (oestrogen) tablets, or small doses of rFSH (Puragon or Gonal-F) are administered in order to prepare the endometrium for implantation. The development of the endometrium is monitored by ultrasound scanning (approximately 1-2 scans). The first ultrasound is usually performed on day 10-12. When the endometrium is thick enough and of the right maturity, a trigger injection is given to better effect ovulation and to change the endometrial receptivity.

The embryos are then thawed for transfer. Progesterone pessaries are almost always used to maintain the endometrium, and needs to be continued for the first 10 weeks of any resulting pregnancy. The embryologist will thaw your embryos so that the age of the embryos corresponds to the maturity of your uterine lining. The exact timing will depend upon the stage at which the embryos were frozen. You are asked to ring the day before your embryo transfer to check the time that the procedure is booked for. Not all embryos survive the freezing, storage and thawing process. The Fertility Nurse/Specialist will notify you if there is a problem.

The embryo transfer procedure and follow-up tests are the same as for IVF embryo transfer described previously.The success rate using frozen embryos is 20% – 40%. The pregnancy rate will depend on the number and quality of embryos transferred, your age and your cause of infertility. If you decide you no longer wish to have your frozen embryos kept for yourselves you have the choice of donating them or having them disposed of. A combination of these choices is also available. If they have not been used after 3 years then Fertility North will contact you to ask your intentions.

What are the risks involved?

These are minimal, but will depend on whether your specialist has organised a ‘natural’ FET cycle or a stimulated FET cycle for you. The risks from a stimulated FET cycle are minimal compared to an IVF/ICSI cycle, as very small doses of medication are used to prepare the endometrium for transfer of the embryo/s. Rarely if the endometrium fails to develop, then the cycle is cancelled and you will be reassessed as to treatment with a different stimulation protocol in your next FET cycle.