Cryopreservation is a technique used by World IVF Centre to freeze and then thaw sperm and embryos for use in vitro fertilization (IVF) cycles. With the availability of frozen embryos, a woman doesn’t need to undergo stimulation by fertility drugs in order to have an embryo transfer during an infertility treatment cycle. When sperm is collected during microsurgery or by other means, and frozen for a subsequent IVF cycle, additional surgery may be avoided.
During the standard course of infertility treatment, hormones are used to stimulate the development of multiple eggs. After these eggs are retrieved and fertilized in the laboratory, there may be more embryos created than can reasonably be transferred to the woman’s uterus. When these “extra” embryos are of good quality, they may be cryopreserved (frozen) so that they may be transferred at a future date. Embryo cryopreservation, which is possible in approximately 25% of IVF cycles, provides the opportunity to have an additional embryo transfer without the inconvenience and expense of a full IVF cycle.
Embryos may be frozen at any stage between day 1 and day 6 after egg retrieval. However, not all embryos are fit for cryopreservation. Unfortunately, some may be damaged by cryopreservation and experience has shown that good quality of embryos are far more likely than others to survive and be capable of further development after freezing. Embryos that divide slowly, or are irregular in other ways, do not survive well after cryopreservation and, therefore, are not frozen.
After placing the embryos in a cryoprotectant solution, they are frozen in a computer-controlled device designed specifically for embryo cryopreservation. Long-term embryo storage is in liquid nitrogen, at a temperature of -1960°C.
Cryopreserved embryos are replaced during either a natural menstrual cycle or a hormonally controlled cycle. Considerable care is taken to minimize the possibility of damage caused by cryopreservation. Depending on the embryo stage at the time of freezing, 60 to 90 % survive the freezing/thawing process. The pregnancy rate after transfer of these embryos is similar to that of fresh embryos.
Extended periods of storage in liquid nitrogen have no apparent affect on their viability. Embryos thawed after several years of cryostorage fare as well as those frozen for only one or two months having similar results. Since 1983, the cryopreservation procedure has resulted in the birth of thousands of babies worldwide. With this extensive experience, there have been no reports of any increase in birth defects as a result of cryopreservation.
With the latest cryopreservation protocols, oocyte cryopreservation is doing equally well and babies are born from embryos formed from cryopreserved eggs.