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Embryo freezing

Some people who are having fertility treatment have leftover embryos after their IVF cycle. Find out how your embryos can be frozen for use in later treatment or to donate to research, training or someone else.

Why do people freeze embryos?

Often with in vitro fertilisation (IVF) or Intracytoplasmic sperm injection (ICSI) treatment, there may be good quality embryos left over after embryo transfer. Instead of discarding them, there is  the option to freeze them to use in the future (in case treatment doesn’t work for example, or to try for a sibling).

Embryos can also be frozen to preserve  fertility so it may be possible to have a baby at a later date.   

Find out more about preserving your fertility

Is embryo freezing for me?

You may wish to consider freezing your embryos if:

  • You want the option of using your embryos in the future (rather than having a further fresh IVF or ICSI cycle).
  • Your treatment needs to be cancelled after egg collection (for example, if you over respond to fertility drugs). You should be offered the opportunity to have any suitable embryos frozen to use later..
  • You have a condition, or are facing medical treatment for a condition, that might affect your fertility (embryo freezing is currently the most effective way for women to preserve their fertility, although it is possible to freeze eggs). Please note that, depending on where you live, you may not be able to have embryo freezing on the NHS.
  • You are at risk of injury or death (for example you’re a member of the Armed Forces who is being deployed to a war zone) and you want to create and freeze embryos with your partner.
  • If you're a female transitioning to a male, you may want to preserve your fertility before you start hormone therapy or have reconstructive surgery. Both treatments can lead to the partial or total loss of your fertility. Read more information for Transsexual and non binary people seeking treatment.

Find out more about preserving your fertility

What happens when embryos are frozen?

Not all embryos are suitable for freezing so only good quality embryos will be chosen to freeze. Embryos can be frozen at different stages of their development – when they’re just a single cell, at the two to eight cell stage or later in their development (called the blastocyst stage).

Find out more about the development stages of embryos

The embryos are put in a special solution containing substances (cryoprotectants) , which help to draw water out from the embryo and provide protection in the cells. This protects them from damage caused by ice crystals forming. They’re then frozen, either by cooling them slowly or fast freezing (vitrification) and stored in tanks of liquid nitrogen until you’re ready to use them.

How long can my embryos be stored for?

The standard storage period for embryos is normally 10 years, although women in certain circumstances can store their embryos for up to 55 years. Your clinician will be able to explain whether you can do this.

You must let the clinic know if you change address. This is extremely  important as if the clinic can’t reach you at the end of your agreed storage term, they may have to take your embryos out of storage and allow them to perish.

If you have the option to store for 55 years, you’ll need to confirm that you want to continue storing your embryos and your doctor will need to confirm that you’re eligible to do so. Again, it's vital that you stay in touch with your clinic to prevent your embryos from being discarded if your storage runs out.

How much control do I have over what happens to my embryos?

Before your embryos are frozen, it’s very important you give your informed consent by signing the relevant consent forms. These will explain:

  • how long you want the embryos to be stored for
  • what should happen to your embryos if you or your partner were to die or become unable to make decisions for yourself
  • whether the embryos are to be used for your own treatment only, or whether they can be donated for someone else’s treatment, or used for research
  • any other conditions you may have for the use of your embryos.

Find out more about giving consent

What if one of us changes our mind about using or donating embryos?

You, your partner or the donor(s) (if applicable) can vary or withdraw consent at any time before the embryos are used in treatment or research. If your partner withdraws their consent then your embryos cannot be used in treatment. 

If one person withdraws consent (either the person who provided the eggs or the sperm) then there maybe a ‘cooling-off’ period of up to a year. If after this time your partner or the donor(s) till doesn’t want the embryos to be used, they’ll be removed from storage and allowed to perish. 

What happens when I want to use them?

The exact procedure for using your frozen embryos varies depending on your personal circumstances and your clinic.

The initial steps depend on whether you are ovulating regularly. If your periods are regular, your doctor may suggest having the embryo transferred to your womb with no fertility drugs. In this case, ultrasound scans may be used to check the lining of your womb. Urine or blood tests may be used to check when you’re ovulating (releasing an egg), which indicates that the lining of your womb will be ready to receive the embryo.

If your periods aren’t regular, or you don’t have them at all, your doctor may suggest using drugs to suppress your natural cycle and trigger a ‘false’ period. You are then given medication to help prepare the womb lining for an embryo.

When the timing’s right, the clinic’s embryologist (embryo specialist) will thaw your embryos and usually transfer one embryo to your womb (three embryos can be transferred in exceptional circumstances if you’re over 40).

Find out more about embryo transfer

How successful is embryo freezing?

Success rates for IVF using frozen embryos have been increasing year on year. 

For the latest statistics on surgical embryo freezing, visit our Research and data page

Does freezing damage the embryos?

Sadly, not all embryos will survive the freezing and thawing process and very occasionally no embryos will survive.

It’s not uncommon for those embryos that do survive to lose a cell or two. In many cases the embryo will recover and continue to develop.  The clinic will talk to you about whether the embryo is suitable to be transferred.

How safe is it to use frozen embryos in treatment?

It’s just as safe as using fresh embryos in treatment. The main risk is having a multiple birth (twins or triplets), which can pose serious health risks to both mum and babies. You can reduce your risk of having a multiple birth by transferring only one embryo to the womb, a process known as elective single embryo transfer or eSET.

Find out more about embryo transfer

Find out more about the risks of multiple births

Clinics are required to offer counselling to all patients undergoing this process – it can be particularly helpful at this time.

Find out more about getting emotional support

What if I don’t use my embryos or I have some left over?

You can either discard them or donate them (to someone else or for use in research or training). In both cases, you and your partner/donor will need to give your consent in writing, Your clinic should provide the relevant forms.  

Donate them to someone else: Give someone the most precious gift of all by donating your embryos to someone in need. 

Find out more about donating your embryos

Donate them to research: Research on eggs, sperm and embryos is invaluable in helping scientists to understand causes of infertility and develop new treatments.

Find out more about donating to research

Donate them to training: Trainee embryologists need embryos to practice techniques, such as removing cells from embryos and mastering the freezing/thawing process.

Discard them: Some people prefer to discard their embryos. Embryos that are no longer needed are simply removed from the freezer and allowed to perish naturally in warmer temperatures or water.

Review date: 9 February 2024