Any excess healthy embryos from IVF treatment are usually frozen, in case more than one embryo transfer is needed to achieve a pregnancy, or you are trying to achieve a subsequent pregnancy. Freezing embryos – or cryopreservation – takes place for around 60% of all patients having IVF treatment, and frozen embryo transfers (FETs) account for many IVF births at Queensland Fertility Group.
What is a Frozen Embryo Transfer (FET)?
If we obtain more than two embryos during an IVF cycle (this does not always happen) we’ll usually recommend transferring one and freezing any additional suitable embryos. If you do not become pregnant with your first embryo transfer, we can then thaw and transfer another embryo. This is called a Frozen Embryo Transfer (FET), and means you won’t have to undergo another full cycle of hormone stimulation and egg collection.
How are embryos frozen?
Embryos can be frozen from day 2 (four-cell stage) to day 5-6 (blastocyst). Embryos are rapidly frozen using a procedure known as vitrification; day 2-3 embryos may also be frozen using a slow-freezing procedure. They are then stored in tanks filled with liquid nitrogen, which keeps the temperature at -196°C.
Why do we freeze embryos?
Embryo freezing gives you more opportunities for a pregnancy from each hormone stimulation cycle and egg collection.
During a typical IVF cycle we may create more than one or two embryos, but we don't transfer them all as there are serious risks involved with multiple pregnancies. For example, if we get six normal embryos, we usually only transfer one, and freeze the others.
If you have additional embryos you don’t want to use yourself, you may choose to donate your frozen embryos to another couple who can’t conceive with their own. Your fertility specialist can discuss all your options with you at the appropriate time.
Success rates with frozen embryo transfers
At Queensland Fertility Group, many successful births through IVF have come from a Frozen Embryo Transfer (FET). Success rates depend mainly on the age of the woman’s eggs when the embryos are frozen. You have the same chances of conception as the age you were (or the donor was) when the embryo was frozen. You can find clinical pregnancy rates for FETs on our success rates page.
When do you freeze all embryos?
Freezing all embryos following an IVF cycle, and transferring them later as part of a normal menstrual cycle, is routinely used for patients who have extremely high hormone levels to prevent possible Ovarian Hyper Stimulation Syndrome. Research has indicated that the womb may be less receptive to an embryo immediately after a stimulated IVF cycle if reproductive hormone levels are high or unstable. It has been proposed that high hormone concentrations (that can result from the fertility drugs used in IVF treatment) may affect the function of the lining of the womb. Research continues into the overall benefit of freezing all embryos, compared with the standard approach of undertaking a transfer during the stimulated IVF cycle.
To find out more about frozen embryo transfers, or to book an appointment with a Queensland Fertility Group Fertility Specialist, call 1800 111 483 to speak with an experienced fertility consultant.