Vitrification is a fast freeze process for eggs and embryos.
During the in vitro fertilization process, there are often more excellent quality embryos that develop than can be transferred into the woman’s uterus at the time of her fresh transfer. In these situations, we have the ability to offer our patients the opportunity to freeze these “extra” excellent quality embryos.
Embryo freezing, sometimes called “cryopreservation” or “vitrification” allows patients fortunate enough to have excess embryos to have another chance for pregnancy without having to go through another ovarian stimulation and oocyte retrieval, and without having to buy more expensive stimulation medications and take shots.
Among those embryos that continue to divide, there are some that meet specific criteria that allow them to be successfully frozen. These embryos are usually frozen (vitrified) on day 5 or on day 6 after the eggs have been retrieved. Vitrification of these excess embryos provides an opportunity for achieving pregnancy at another time in the future, thus increasing the number of potential transfers from a single retrieval.
There are several methods that have been used for freezing embryos.
They can be divided into two categories; the slow-freezing process and the vitrification (quick freeze) process. During the slow-freeze process, embryos are exposed to cryoprotectant solutions (an antifreeze product) for a longer period of time while the temperature of the embryo is reduced at a specified rate until it is fully frozen. With vitrification, embryos are exposed to a higher concentration of cryoprotectant solutions for a very short time and are then frozen very quickly.
The general principle behind both processes is very similar. Basically, an embryo is exposed to a cryoprotectant freezing solution in order to remove all of the water from the cells. While this is being done, the temperature of the embryo is lowered, allowing it to be completely frozen.
All frozen embryos are stored in liquid nitrogen, which has a temperature of -196 degrees C (-320 degrees F). Storage at this extremely cold temperature halts all metabolism of the embryo, allowing embryos to be safely stored for an indefinite period of time.