| Cryopreservation: is the freezing of oocytes, sperm or embryos for future use. Cryopreservation enables patients to save their gametes (oocytes and sperm) or embryos for future attempts at pregnancy. The cryopreservation process includes exposing the gametes or embryos to a cryoprotectant similar to car antifreeze. Water in the embryos is replaced with cryoprotectant that prevents ice crystals from forming inside the gametes or embryos, as this would destroy them. The addition of sucrose (common table sugar) also reduces the osmotic stress to an embryo during the freezing and thawing process.
Sperm Cryopreservation: Human sperm cryopreservation has been available since the late 1950's. Perhaps surprisingly, techniques used to freeze human sperm have changed very little. The RSC currently freezes and stores sperm for autoconservation. There is long and short-term autoconservation. Long-term cryopreservation is available to men who are undergoing possible sterility treatments such as 1) radio- or chemotherapy or 2) vasectomy. Short-term cryopreservation is available for patients who might not be able to collect on the day of their wife's fertility treatment do to 1) stress on demand or 2) absence do to job or other conflicts. Short-term cryopreservation can also be used to store surgically retrieved 1) epididymal or testicular sperm or 2) electroejaculated sperm from spinal cord injured men for use in a later IVF cycles. Approximately, 50% of the motile sperm survive the freeze/thaw process.
The RSC also orders sperm and stores sperm from donor sperm banks for use on patients for donor sperm insemination. Donor sperm insemination is available to couples 1) whose husband has absent or very poor sperm parameters or 2) single woman.
Oocyte Cryopreservation: There has long been an interest in oocyte autoconservation. Until recently, however, very poor freeze/thaw survival rates have prevented this as being a successful option. Improvements in cryotechnology have recently made this an acceptable but still experimental alternative. Similar to sperm cryopreservation, oocyte cryopreservation is an exciting option to patients undergoing sterility treatments such as 1) radio- or chemotherapy or 2) ovariectomy. In addition, freezing oocytes may provide an option to 1) couples who are uncomfortable with ethical or religious idea of freezing embryos 2) women have not yet found a partner and want to freeze their oocytes to stop the "biological clock." An even more novel procedure is the cryopreservation of ovarian cortical tissue containing hundreds or more immature oocytes. This tissue can then be thawed and either re-transplanted or underdeveloped oocytes matured in vitro followed by in vitro fertilization. Although this procedure holds incredible promise, to date no pregnancies have established using this technique.
 Embryo Cryopreservation: The cryopreservation of supernumerary embryos (those that are not transferred) is a wonderful option for patients should their fresh cycle not be successful, or should they decide to have another child after a successful cycle. Cryopreservation is also an economical way to have several attempts at pregnancy using the frozen embryos, as a "frozen cycle" is far less costly than a "fresh cycle." Currently, at the RSC culture all embryos are cultured to the blastocyst stage prior to cryopreservation. This insures that only good quality potential embryos are frozen. Survival rates of good quality blastocysts frozen by the latest slow freezing protocols are approximately 85%. Overall pregnancy rates with these embryos are approximately 25-65% (pic left of frozen/thawed day 5 blastocyst). |
