Egg, Sperm or embryo freezing may be required as part of a fertility treatment cycle or for fertility preservation purposes.
Before we can freeze any eggs, sperm or embryos we must screen for HIV, Hepatitis B and Hepatitis C. To do this we need one blood sample and this can be taken at your GP practice or in the Centre.
In order to obtain eggs for freezing a full IVF cycle must be undertaken.
After your egg recovery only the mature eggs are prepared before being frozen and placed in storage tanks. Not all eggs collected at the egg recovery may be suitable for freezing as they may not be mature enough and will not survive the processes. Eggs are the largest cells in the human body which make freezing and thawing quite difficult. Approximately 70% of the eggs will survive thawing.
The success rates have improved in recent years as a result of using a technique called Vitrification. Previously ice crystals formed during the freezing process however the Vitrification technique prevents ice formation as the egg is dehydrated to get rid of as much water as possible then plunged into liquid nitrogen.
When the eggs are to be used in a treatment cycle they will be removed from the storage tanks, thawed and then ICSI will be undertaken on the surviving eggs.
It is important not to have sex or masturbate for at least 3 days but no longer than 7 days before producing a sample for freezing. If you live near the hospital you can produce the sample at home, as long as it can be delivered to the laboratory within 1 hour, otherwise we have designated rooms available for men to use to produce samples.
The sample will be analysed in a similar manner to the routine semen analysis then mixed with a solution to protect the sperm through the process of freezing before being divided in small amounts into straws for freezing. The number of straws stored will depend on the volume of the sample.
A few days later one straw will be thawed to test how well the sample has survived. This information will enable the laboratory to assess the number of straws needed for treatment. More than one sperm sample may need to be frozen depending on the quality.
The survival of sperm after freezing is highly variable and more than one sample may be required. Freezing and thawing can reduce the quality of a semen sample and, in a very few cases, freezing may not be successful.
Should you wish to freeze good quality embryos following your IVF/ICSI cycle you will have an opportunity to do so usually when the embryos are at blastocyst stage.
The success rates have improved in recent years as a result of using a technique called Vitrification. Previously ice crystals formed during the freezing process however the Vitrification technique prevents ice formation as the embryo is dehydrated to get rid of as much water as possible then plunged into liquid nitrogen. On average we have a survival rate of at least 90%, however, there is a risk that there will be no surviving embryos available for replacement following thawing.
Frozen Embryo Replacement
The replacement of frozen embryos can be undertaken at any time and we will discuss all options with you and organise a treatment cycle whenever you wish. If you have embryos stored that are at blastocyst stage (day 5) we would suggest to replace a single embryo. In some cases we need to thaw more than one embryo, depending on the quality of each embryo.
If you have embryos frozen before day 5 stage we may suggest thawing several of them and allowing them to develop in the lab for a few days before transfer to enable us to determine which embryo has the best potential to implant. In some cases we can even refreeze good quality embryos that develop if we have more than is required. All options will be discussed with you and our Embryology lab team prior any embryos being thawed.
If you have embryos in storage you no longer need for your own treatment you may find it difficult to know what to do next. Whether or not your treatment was successful letting go of your embryos can be hard. The HFEA website has an information leaflet which you should read at this time. https://www.hfea.gov.uk/media/2514/i-have-remaining-embryos-what-are-my-options.pdf