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The embryo storage process

A clinician handling frozen embryosWhat happens when embryos are frozen?

Step 1. Before the procedure can take place, the people involved will have to give consent:

  • If you are using your own eggs and your partner’s sperm - you will both have to give written consent.


  • If you are using donated sperm or eggs - both the donor and you or your partner (whoever provided the sperm or eggs) will have to give consent.

Step 2.  Before embryos are frozen, your clinic will screen both people who provided the eggs and sperm used to create the embryos for infectious diseases such as HIV, Hepatitis B & C.

Step 3. During treatment, the unused embryos are frozen and then stored in tanks of liquid nitrogen. A liquid called a cryoprotectant is added to protect the embryos during freezing.

Step 4. Not all embryos survive freezing and thawing, so when you come to your next treatment cycle, your clinic may advise you to have more embryos thawed than can be transferred.

In the standard freezing method, embryos are slowly frozen down to -196 degrees celcius.

A method of embryo storage has been developed called ‘vitrification’. This is a fast freeze process – the embryo undergoes instantaneous ‘glass-like’ solidification without the damaging formation of ice crystals (which can occur with the standard method of freezing).

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How long can embryos be stored?

Clinican handling stored embryosThe normal maximum period that frozen embryos can be stored is ten years. This may be extended depending on the medical circumstances of the woman undergoing treatment, her partner and/or a donor.

If the embryos were created using donated sperm or eggs, the donors will need to give their consent to extending the storage period.

Storage period times are set out in the Human Fertilisation and Embryology (HFE) Act 1990 (as amended by the HFE Act 2008).

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What happens at the end of the storage time?

It is important to keep in contact with your clinic, otherwise your wishes may not be taken into account when the storage period ends.

  • After the embryos are put in storage, you must tell the clinic if either you or your partner changes address.

    If the clinic can’t contact you when the period finishes, they mayl take the embryos out of storage and allow them to perish.
  • If either of you, or a donor, withdraws consent to storage of the embryos and you do not agree on what should happen to them then there will be a ‘cooling-off’ period of up to a year (during which the embryos can remain in storage) which will allow you to come to a decision.
  •  Before the end of the storage period, the clinic will contact you and ask what you want to do next, such as extend the storage period, allow the embryos to perish or donate them for research or to another patient.
  •  If you’re using donor sperm or eggs, the donor should also keep in contact with the clinic as their wishes and consent also has to be taken into consideration.

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What happens when frozen embryos are used?

The exact procedure for using your frozen embryos varies, depending on your personal circumstances and the type of treatment your clinic offers:

Step 1. The initial steps depend on whether you are ovulating regularly:

  • If your periods are regular and your clinic offers treatment every day - your doctor may suggest using a natural cycle. In this case, ultrasound scans may be used to check your developing eggs and the thickness of the endometrium lining of your uterus and urine or blood tests to check when you are ovulating (releasing an egg).


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

Step 2. When the endometrium is at its most receptive, the clinic's embryologist thaws the embryos. One or two will then be transferred.

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Page last updated: 09 January 2013

Who offers embryo freezing and storage?

To find the clinic nearest to you that offers embryo storage, use the advanced search on our Choose a Fertility Clinic database.