FET (Frozen Embryo Transfer)

Freezing Embryos

Any excess healthy embryos from the IVF process can be frozen, in case more than one treatment cycle is needed. Freezing embryos, also known as cryopreservation, takes place for some 60% of all patients having IVF treatment – and frozen embryo transfers accounts for around 50% of all IVF births in our program.

Why do we freeze embryos?

Embryo freezing provides more opportunities for a pregnancy from each IVF stimulated cycle. For example, if a number of normal embryos are obtained in an IVF cycle, we might suggest transferring one or two of them and freezing the other four or five. This would generally allow further embryo transfers in later cycles without the need to undergo a full stimulated IVF cycle if pregnancy did not occur in the first cycle. If a baby is conceived in the stimulated IVF cycle then the frozen embryos can be used subsequently to try for another pregnancy without the need for further hormone stimulation

Embryo freezing gives more opportunities for a pregnancy for each hormone stimulation cycle and egg collection.

During a typical IVF cycle, we’ll be able to create more than one embryo, however there are serious risks associated with multiple pregnancies, so generally we won’t transfer more than one embryo at a time.

For example, if we manage to obtain two or three normal embryos (this does not always happen) we’ll usually recommend transferring one, and freezing the others. If you do not become pregnant in that first cycle, we can transfer another embryo.

This is called a Frozen Embryo Transfer (FET), and means you won’t have to undergo another cycle of hormone stimulation and egg collection.

Storing frozen embryos

When you go through an IVF treatment cycle any excess embryos will be stored where they will be kept frozen in cryostorage until you decide to either use, donate or discard them.

How does embryo freezing work?

Embryos can be frozen from Day 2 (four cell stage) to Day 5 (Blastocyst). They are placed in thin plastic straws, sealed at both ends, and labelled with your name and identification number.

They then go into a freezing machine, where the temperature rapidly drops to -150° Celsius. The straws are then placed in goblets, and put into tanks filled with liquid nitrogen, which keeps the temperature at -196° Celsius.

Success rates with frozen embryos

many of our births, over many years, have come from the transfer of frozen and thawed embryos. On average the success rate is about 30%, but this mainly depends on the age of the woman’s eggs when the embryos are frozen.

So, if you were to freeze your embryos in your first IVF cycle at the age of 38, and then use them when you’re 42, your fertility chance will be relative to that of a 38-year-old woman rather than a 42-year-old.

What to do with any remaining embryos?

Once you feel that your family is complete, and you have no further personal use for your frozen embryos, you may decide to donate them to another couple who are unable to conceive with their own embryos. Your specialist can discuss all your options with you

Freezing embryos for fertility preservation

If you or your partner is undergoing fertility treatment for a serious illness or cancer you might consider freezing embryos for future pregnancy attempts.