Cryopreservation refers to the storage of a living organism at ultra- low-temperature such that it can be revived and restored to the same living state as before it was stored.
Embryo cryopreservation (the process of freezing, storage and thawing embryos) can enhance pregnancy rates by allowing excess embryos not replaced in a fresh embryo transfer to be stored for future use.
Embryo freezing may also be performed when a fresh embryo transfer is not performed for any of the following reasons:
Embryos are placed into straws or vials containing anti-freeze or cryoprotectant solutions. These are transferred to a programmable biological freezer which is used to achieve a controlled slow rate of cooling. During cooling, cells dehydrate and as the temperature is reduced, more ice forms and water is removed gradually from the cells. Slow cooling is continued to ~ -35Â°C at which point embryos are rapidly cooled by plunging into liquid nitrogen (-196Â°C). Embryos are kept in storage tanks of liquid nitrogen until thawing is performed.
Vitrification in IVF can allow freezing of spare embryos with better post-thaw survival rates and higher pregnancy and live birth rates from the frozen embryo transfer cycles. We started vitrification of embryos in our IVF lab and have seen excellent post-thaw embryo survival and high pregnancy rates after frozen embryo transfer procedures.
Semen freezing is useful for men who find it difficult to ejaculate on demand which may result in their inability to produce a sample on the day of egg collection.
Sperm from two sources can be frozen: from ejaculates or from fluid extracted in the operating room during surgical procedures (vasal, epididymal and testicular sperm specimens). The sperm is usually frozen for a period of one year; at that time, future arrangements are discussed. It is generally believed that sperm that have been through the freeze-thaw process are no more likely to result in birth defects than freshly ejaculated sperm.