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Embryo Cryopreservation – Information for Patients

Patient information A-Z

Cambridge IVF logo and strapline 'creating your future'.
A person freezing embryos in a container with blue gloves on
Five photos of embryos under a microscope and a photo of a baby

What is Cryopreservation?

Cryopreservation or ‘Freezing’ of embryos takes place on day 5 and 6 of your treatment cycle after your embryo transfer in cases where we have 1 or more good quality embryos remaining.

By storing embryos we can then thaw them out and transfer them back to you in the same way as we did in your ‘fresh’ treatment cycle. Freezing and thawing of embryos allows us to extend the number of chances you have to become pregnant from one egg collection procedure.

At Cambridge IVF we use a technique called ‘vitrification’ to rapidly freeze any good quality blastocysts (advanced day 5 or day 6 embryos) which are remaining after your embryo transfer procedure. Any embryo which has the capacity to form a good quality blastocyst certainly has the potential to form a pregnancy. We freeze using this technique at the blastocyst stage as evidence suggests that vitrification is the most effective method to successfully freeze your blastocysts.

Cambridge IVF has a state of the art Cryostorage facility on site. Embryos are stored at very low (-196oC) temperatures using liquid nitrogen or its vapour.

How Does the Process Work?

Before we can store your embryos we need the consent of both the male and female person who provided the gametes. This is a legal requirement and we will ask you to consider and complete a series of electronic consent forms before you proceed to treatment.

There are 4 key areas we need to consider when we take legal consent to the storage of your embryos, these are:

  1. What should happen to the stored embryos in the event of your death or mental incapacitation? It is important that we know your wishes before we store your embryos. It may be possible to register a deceased partner as the parent of a child, but all of these implications must be discussed with you prior to treatment.
  2. How long you wish to consent for your embryos to be stored. The statutory storage period for which embryos can be frozen is up to 10 years. You can of course decide to freeze them for a shorter period. You can also at any time prior to the embryos being transferred decide that you no longer want them to be kept in storage – for more information on the implications of this, please see our patient information on ‘Consent to treatment’ in particular the section on ‘Withdrawing, varying and restricting consent’. In certain circumstances, the law allows embryos to be stored for up to 55 years. For this to be applicable, a registered medical practitioner will need to certify in writing that the patient is prematurely infertile or likely to become prematurely infertile. This written opinion will need to be renewed at least every 10 years during the 55 year storage period. We believe that the majority of patients are unlikely to need to freeze their embryos for longer than 10 years. However, if you think your situation is such that this is applicable to you, then our medical staff will be happy to discuss this with you.
  3. The law does not allow us to keep your gametes or embryos in storage beyond the date you have consented to. We will be in touch with you a few months before the end of the storage period to find out what you wish us to do. It is important that you keep in touch with us, in particular that you notify us of any change of address. If the storage limit is up, and you have not consented to extending this limit, we are obliged by law to let any stored embryos perish, even if we have not been able to trace you first.
  4. If you wish you can consent to the use of your embryos in research. In certain circumstances you may donate them for the use of other people for their treatment if you decide that you do not need the embryos for your own use anymore.

It is important that you answer these questions as clearly as you can leaving nothing open to interpretation as your wishes on these issues are required by law before we freeze your embryos.

Blastocyst Vitrification

Good quality surplus blastocysts can be frozen on day 5 following your embryo transfer. We use a process called vitrification to rapidly freeze your blastocysts which we then store in our Cryostore for you to use at any time in the future within the time period you have consented to.

On day 5 and day 6 of your cycle we will look at all the remaining embryos and decide if any of them are strong enough to be frozen and we will let you know at the time of transfer how many are suitable. Of course its your choice, you don’t have to have them frozen if you don’t want to, we will carry out your wishes either way but you should spend some time before your ET deciding what you would like to do if you do have embryos available to be vitrified.

If your embryo transfer is on day 3 and there are some embryos remaining we can culture these on for 2 more days to see if any blastocysts form and freeze any which are of suitable quality for you at that time.

Which embryos could we freeze?

Freezing and thawing can cause damage to the cells of an embryo. This means that only best quality embryos are suitable for freezing as poor quality embryos very rarely survive thawing. We use the vitrification technique on blastocysts to minimise the chances of an embryo we store failing to survive the freeze / thaw process.

What is the likelihood of embryos surviving the procedure?

Our data on vitrification and thawing survival rates demonstrates that we achieve survival rates of around 90%. In some cases some of the cells or all of the cells within the blastocysts may not survive. This is unpredictable and can be patient specific.

Do the surviving blastocysts resume development after thawing?

Once the blastocysts are thawed, our policy is to place them in culture medium for approximately 2-4 hours prior to your transfer. This allows us to determine whether the surviving embryos are capable of resuming development.

How many thawed blastocysts are required to optimise the chance success?

The chances of success with frozen thawed blastocysts are comparable to the success rates with a fresh blastocyst transfer. As blastocysts are known to survive vitrification very well we recommend that you consider freezing any good quality blastocysts we have remaining or are able to grow on after your embryo transfer. The number of blastocysts to thaw will be discussed with you during your treatment in order to optimise the chance of achieving a pregnancy but also minimise the risk of a multiple pregnancy. There are several factors to consider when considering the number of blastocysts to transfer, such as female age, treatment history and embryo quality.

What are the risks to a child born using a frozen blastocyst?

There is no evidence that any babies resulting from thawed embryos have an increased risk of harm or abnormality or that the pregnancy itself is at more risk because a frozen / thawed blastocyst has been used. Cambridge IVF constantly monitor our results and pass on information to the HFEA which allows high power data analysis to be carried out at a national level to ensure that we continue to operate safely and in as informed an environment as possible.

What do we do if we want embryos frozen?

Where applicable, both partners must give consent to freezing and storage of your blastocysts. At the time of your embryo transfer we will discuss with you the quality of any remaining embryos so it is important we know your wishes before this point in your treatment cycle. The embryologist will let you know if freezing is recommended based on your own unique treatment cycle results. Freezing of any suitable embryos will be done on day 5, we will also freeze top quality blastocysts on day 6. Blood samples will have been taken from both partners, to test for HIV and Hepatitis B & C. The results of these tests need to have returned before we are able to store your blastocysts.

The tests are performed to allow us to store your blastocysts appropriately in a screened or viral positive storage facility as appropriate and may be funded by the NHS or in some cases you may have to pay for them. The cost for the tests in such circumstances is available in the Cambridge IVF schedule of fees. Additional tests may be performed depending on your personal circumstances and you will be informed if we plan to carry out further testing during your appointment. If any of the test results return indicating an infection we will notify you and arrange an appointment for you to see a medical practitioner.

Could anything go wrong with our Storage?

We do everything we can to maintain a high quality cryostore here at Cambridge IVF. We have a system in place that monitors the cryostore continually and will alert us immediately if there is the slightest suggestion of a problem. We use a high security storage system to reduce the theoretical risks of cross contamination between samples. Even with our exacting standards and commitment to quality in everything we do, we cannot provide a guarantee that your samples may not be affected in the event of an ‘act of god’, civil disturbance, catastrophic equipment failure or any other unexpected and abnormal occurrence which may affect our service or facilities.

Clinical Results

We are very proud of our success rates at Cambridge IVF. Our results are in line with or exceed latest published national averages. We excel in cryobiology and our success rates for frozen embryo transfer are comparable with our results using fresh embryos:

Bar chart showing the national average and Cambridge IVF's clinical pregnancy per frozen embryo transfer between 2020 and 2021
Clinical pregnancy per frozen embryo transfer (2020-2021)

Our embryologists are State Registered with the Health and Care Professions Council (HCPC) and have all attained certification with the Association of Clinical Embryologists having successfully completed their internationally acclaimed training scheme.

We have put together the team based not only on the skill of the scientists and their depth of knowledge but also their desire to make Cambridge IVF a patient focused and friendly unit which not only excels clinically but achieves this whilst maintaining a close and open relationship with our patients.

Comment on Witnessing

We are all very aware there have been IVF mix-ups in other clinics in the UK and across the world. Cambridge IVF has taken every step possible to minimise the risk of mix up occurring here and we are very proud that since we opened in 2011 we have never had a mix up event occur.

In addition to stringent checking and procedural controls being in place, we have invested in an electronic system called RI Witness which provides a further layer of transparent and auditable protection against the mixing of incorrect sperm and eggs or transfer of the incorrect embryos in your cycle. We are not saying we are likely to have made a mistake without it, this could not be further from the truth but we do believe in making our processes as safe and risk free as possible and we believe that RI Witness ensures this. We also believe it is right to inform you that such risks exist and we do everything possible to reduce them.

We hope you have found this booklet informative and interesting. We realise we may not have covered all of your questions so if you do have any other queries we are here to help so please contact us via any of the means below:

How to get in Touch

Cambridge IVF
Kefford House
Maris Lane

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Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151