When you undergo your IVF treatment you may find after embryo transfer that there are some extra embryos that are suitable for freezing.
Why freeze embryos?
Using stored embryos for future treatment avoids the need for further stimulation, egg collection and fertilisation.
Frozen embryos can be transferred in two types of treatment cycle: if you ovulate reliably embryos can be replaced in your natural cycle, otherwise you will need an ‘artificial’ cycle using drug therapy.
How are embryos frozen and stored?
The cryopreservation process uses a series of specially designed solutions that work to quickly dehydrate and stabilise the embryos before they are plunged directly into liquid nitrogen; this is known as vitrification.
Embryos are frozen in small straws that are stored in large tanks of liquid nitrogen at minus 196 degrees Celsius. All tanks are fitted with alarms that notify us 24 hours a day of any change in temperature that may require our attention.
Will my embryos be frozen?
If there are good quality embryos remaining after your fresh embryo transfer, we will continue to culture the remaining embryos to the blastocyst stage of development prior to freezing. Any good quality blastocysts that have developed can be frozen for future use.
Only the best grade embryos have the potential to withstand the freezing process, which is somewhat stressful to the cells. On average 95% of embryos survive freezing and thawing.
Embryo freezing should be regarded as a bonus: just over half of couples will have embryos frozen in a treatment cycle.
How successful is freezing embryos?
Pregnancy rates for frozen embryos transfers are slightly lower than for fresh embryo transfers, but depend on the number and quality of embryos frozen. Typically they are about 35% per embryo transfer.