Embryo cryopreservation (freezing) is a process to freeze the remaining, supernumerary un-transferred embryos in a liquid nitrogen tank. The gametes of both partners are fertilized and become an embryo, which then undergoes a computerized freezing process. Its temperature is lowered to -196ºC in liquid nitrogen.

No biological activity will happen at this condition. Most of the embryos will not lose its viability for many years. It may be thawed when the couple expects to get pregnant.

As long as the embryos are of satisfactory quality, these un-replaced embryos are frozen so that they can be used for another cycle if the current cycle fails or for future pregnancy if a subsequent child will be desired some years later.

However during the process of cryopreservation, about 20 - 25% of embryos cannot endure trauma or cannot sustain their viability after thawing. Among the other 80% of embryos that survive, individual implantation rates are approximately two-thirds of those in the same egg retrieval cycle that have not previously been frozen.

Please be aware that only a portion of the supernumerary embryos that are of average quality can be frozen.

The couple will be notified by letter of the number of embryos which could be frozen. The various options concerning the fate of supernumerary embryos will be discussed with doctor before starting treatment.