What is embryo cryopreservation?
Cryopreservation is a process that renders possible the preservation of embryos obtained during an IVF treatment for a later use. After being protected from the devastating effects of water crystallization during the freezing process by incubation in cryoprotectants, the embryos are rapidly frozen and kept at very low temperatures (-196^oC) until use. Viability of these embryos can thereby be preserved for years.

Why choose embryo cryopreservation?
Cryopreservation of surplus embryos can particularly be useful in some situations namely:

To increase the likelihood of achieving a pregnancy for a given IVF treatment

For a second pregnancy from the same IVF treatment

When, for any reason, a fresh embryo transfer is not an option

Facts
It is noteworthy that embryo cryopreservation is particularly efficient (survival rates of about 75%) when the embryos are growing well. Therefore, not every single embryo is a good candidate for cryopreservation. As a result, the success of the procedure is intimately bounded to the embryo selection before freezing.