Since most IVF programmes superovulate patients to grow many eggs, there are often many embryos. Since the risk of multiple pregnancy increases with the number of embryos transferred. It is now also possible to freeze these embryos and store them in liquid nitrogen. These stored embryos can then be used later for the same patient - so that she can have another embryo transfer cycle done without having to go through superovulation and egg collection all over again. However, since it is worthwhile freezing only good quality embryos, the option of freezing is a "bonus" which is available to only about 30% of all IVF patients. About 70-80% of all embryos frozen survive the freezing thaw process. It is reassuring to know that the risk of defects is not increased as a result of freezing. These frozen embryos can be stored for as long as is needed - even for many years. When they are in liquid nitrogen, at a temperature of -196 C, they are in a state of suspended animation, and all metabolic activity at this low temperature stops, so that a frozen embryo is like Sleeping Beauty!
Once stored, embryos can be used by the couple during a later treatment cycle, donated to another couple or removed from storage. These options should only be undertaken after considerable discussion. The couple must give written consent to storage and their future use. It is very important that these are completed accurately as any inconsistencies in the couples’ consent forms may make the storage of the embryos invalid. Patients are also responsible for keeping in touch with the unit and notifying us of any change of address.
About 70-90% of all frozen embryos survive the thawing process. Although some couples may have all of their embryos survive in good condition, others may not have any that survive.