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Embryo vitrification is a cryopreservation process available for human embryos to allow parents to store them for future use. This technique involves very rapid freezing to preserve the integrity of the cell structure and limit damage to the embryo. As long as it is stored in optimal conditions, its chances of surviving the thaw cycle for implantation into a donor can be better than those with other freezing methods. Fertility clinics may offer this option to their patients, and it is also available for non-human animals like horses, where embryo preservation may be used to facilitate distribution of a bloodline.
This process starts with an in vitro fertilization procedure, where an egg harvested from a woman is matched with donor sperm. Several eggs may be fertilized and monitored as they develop to determine which turn into viable embryos. Couples may request immediate implantation of one or more embryos, and can request embryo vitrification to freeze the others for use at another time. This can allow them to try again if the first implantation fails, or to have access to fertilized embryos after cancer treatment or other procedures make a partner infertile.
A lab technician adds a cryoprotectant to the embryo and then flash freezes it in liquid nitrogen by dipping it abruptly. This differs from older methods, where embryos were slowly frozen after being subjected to several rounds of cryoprotectant baths to flush out any remaining water in the cells. Embryo vitrification involves freezing so quickly that ice crystals do not have any opportunity to form, which limits the risk of cell damage. The term “vitrification” is a nod to the lack of crystals, as it references a glass-like state where no individual crystals are allowed to develop.
The frozen embryos can be stored in containers of liquid nitrogen until they are needed or couples decide to donate or discard them. After embryo vitrification, a technician can carefully raise the temperature to thaw out one or more embryos for implantation. They will be allowed to divide and grow in vitro to confirm that they successfully made it through the freezing process and are more likely to do well after implantation.
Success is not guaranteed with embryo vitrification. A number of things can go wrong during the process, especially during freezing and thawing, or while the embryos are in storage. Patients can ask a clinic about its success rate, but should be aware that advances in technology can happen quickly and may make statistics outdated. Some facilities have proprietary methods they use that are unique to their labs and may not be available through other care providers.