Frozen embryo transfer (FET)

lab equipment, mother and daughter playing

Spare embryos from your IVF treatment can be frozen for future use, depending on their quality. Frozen cycles are necessary for those wishing to use their previously stored embryos.

With a stimulated frozen cycle, patients take medication to go through the process of down-regulation. This temporarily shuts down your ovaries and prevents any eggs from being released. You will have a scan on day two or three of your period and start taking medication to prepare your womb for the embryo transfer. A second ultrasound scan at day eight or nine will be performed to check the thickness of your endometrium, the mucous membrane lining the uterus. Once it is of the appropriate thickness, we can start the embryo thawing process and book your transfer.

Embryo thawing and transfer

Embryos are thawed in the laboratory and assessed as to whether they have fully survived the thawing process. Our embryology team will inform you of how well your embryos have survived and if they are of good enough quality for your transfer to take place. Sometimes embryos do not survive the thawing process. If this is the case, you will be offered a follow-up appointment with one of our consultants to discuss the results and further options.

Hopefully, the embryos will then be ready to transfer the same as in a fresh cycle. Our frozen cycle success rates have been improving every year and are now, due to our excellent staff, technique and expertise, just as good as our fresh cycle rates.

What proportion of embryos survive the freezing and thawing process?

We find approximately 80% of frozen embryos survive the freezing/thawing process. This can vary depending on what stage of development the embryos were at when they were frozen and the effect freezing may have on different embryos. The current record was made in 2017, when a healthy baby was born from an embryo that had been in storage for 25 years.

Do frozen embryos deteriorate over time in storage?

Frozen embryos are stored in liquid nitrogen at a temperature of -196°C. This means they are held in a suspended state and do not deteriorate with time in storage.

How many embryos should I thaw for my frozen embryo replacement cycle?

There is no fixed answer because it depends on your individual circumstance: your clinician will advise you based on giving you the best possible chance of pregnancy with each frozen embryo replacement cycle. Not all embryos have the same potential to form a pregnancy, and each one is affected differently by the freeze and thaw process. The number will be tailored to you and your embryos.