Embryo freezing and storage

Freeze and store your embryos until you’re ready to use them. 

During IVF treatment, sometimes more embryos are developed than can be used in a single transfer.  If you’d like us to we can freeze your embryos in case you need another round of treatment, or if you’d like to grow your family in the future. 

What does embryo freezing involve?

When you’re going through IVF treatment, once we’ve fertilised your eggs we’ll talk to you regularly about how your embryos are developing, and we’ll let you know whether there will be any of the right quality left for freezing. If there are, and you’d like us to store them for you they are frozen in the following steps:

• Special vitrification solutions are used to protect them in storage
• Your embryos are placed in straws individually so that we can trace each one
• The straws are frozen in liquid nitrogen at -196C. All storage vessels have temperature alarms which are monitored 24/7

When you’re ready to use your embryos we’ll remove an embryo from storage and carefully warm it. Then, if it’s good enough quality, we’ll prepare it for transfer. We’ll aim to place the embryo into the womb of you or your partner at the right time of the cycle, and timing will depend on the stage of the embryos, i.e whether they’re fertilised eggs, early embryos or blastocysts.

Before embryos are frozen, we ask you to complete consent forms which cover the following:

• How long your embryos can be stored for
• What should happen to embryos if something were to happen to you or your partner
• Whether embryos will be used for your own treatment or for someone else’s (e.g. if donating)
• Any other conditions for the use of the embryos

How long can my embryos be stored for?

The maximum period of time is usually 10 years, but this may differ in certain circumstances such as health conditions and what has been agreed with your clinic – you will specify the storage period when you complete your consent forms. Continued storage is conditional on payment of the annual storage fee.

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

It’s possible for either (or both) partners to withdraw their consent to the use or donation of embryos up to the point of embryo transfer. If there’s a dispute between partners over use or donation, CARE is allowed by law to keep embryos for up to one year (following written notification of consent withdrawal) to allow a ‘cooling off’ period.  If the dispute remains unresolved at the end of this time the embryos must be removed from storage. 

What happens when I want to use them?

Frozen embryos can be transferred in two types of treatment cycle: you can undergo treatment in an ‘artificial’ cycle using hormone therapy, or if you ovulate reliably your embryos could be replaced in your natural cycle. The pregnancy rate is unaffected by the choice and is very good with either option.

Artificial FER uses hormones (oestradiol and progesterone) to prepare your uterus in readiness for embryo transfer. A scan is carried out to check your endometrium has responded effectively to the oestradiol. If it has, then progesterone is given which prepares your endometrium to receive the embryo(s). This timing is precise to ensure the day of transfer is optimal for embryo implantation and growth. The advantages of an artificial FER include more predictability, effectiveness in irregular cycles and a shorter time to transfer as no trial cycle is needed.

In natural cycle FERs it is necessary to undertake a ‘trial’ cycle before an actual FER cycle. It must be possible to detect ovulation hormone surge using ovulation predictors, because this sets the day of the embryo transfer – so natural cycle FER is only suitable for women with regular cycles.

Does freezing damage the embryos?

Not all embryos can survive the stressful vitrification process used in embryo freezing, which involves the embryos passing through a series of solutions followed by storage in liquid nitrogen at –196C.  We expect about 95% of good grade embryos to survive freeze-thawing. Sometimes embryos may lose a few cells but still be considered suitable for embryo transfer, as studies have shown they may still be capable of implanting providing more than half the cells remain intact. The survival and quality of the thawed embryo(s) will be discussed with you at the time of transfer.

How safe is it to use frozen embryos in treatment?

This procedure is as safe as using fresh embryos. The main risk is having multiple births (twins or triplets), which can pose health risks to both mum and babies.

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

If you no longer wish to have treatment but still have embryos in storage, there are several options you may wish to consider:

• Donation to another couple - embryo donation gives hope to people who previously thought there was no treatment available to help them. The donors would not be the legal parents of any child born as a result and would have no obligation to, or rights over, that child. Recipient couples of donated embryos would be the legal parents of any offspring born as a result of treatment.
• Donation for training purposes - CARE occasionally needs embryos for in-house training purposes, for example when introducing new procedures or when training new staff in the standard practices we use. Techniques include ICSI, moving eggs/embryos between dishes, freezing/thawing of embryos and biopsy of embryos. Any training records would be reversibly anonymised by using only your clinic ID number.
• Donation to research – if your CARE clinic participates in research they can provide details of the research projects involved
• Discard embryos – involves removal of embryos from storage and allowing them to perish.

To find out more about embryo freezing, talk to your local clinic or contact us.