Cryopreservation, often called freezing, is a process in which cells are suspended in a solution of salts and a mixture of organic compounds called cryoprotectants, substances known to protect against frost damage, cooled to a very low sub-zero temperature (typically -196 ° C). C). in liquid nitrogen), stored for a while, then heated and regenerated to maintain its normal function.
Cryopreservation of oocytes is a method of preserving unfertilized oocytes, or more commonly called eggs, for fertilization, transfer, donation, destruction or any future disposal.
Eggs can be frozen using traditional slow freeze methods or newer fast freeze methods.
At the Family Fertility Center, cryopreservation of oocytes is performed by a rapid freezing method called vitrification.
In general, only adult oocytes can be frozen, although progressive studies have shown that immature oocytes can be frozen even with lower rates of successful fertilization and growth.
After vitrification, the oocytes are transferred to a series of solutions with increasing concentrations of various cryoprotectants and then snap-frozen.
After freezing, the oocytes are stored in liquid nitrogen (-196 ° C; -321 ° F) at very low temperatures.
If a frozen oocyte is detected before embryo formation, it must be fertilized by injecting it into the sperm, also called an intracytoplasmic sperm injection, because freezing leads to hardening of the oocyte envelope.
Once the discovered oocyte is fertilized, it is treated in a manner similar to that used in the IVF laboratory for non-frozen fertilized oocytes.
Any molten oocyte that is not seen surviving cannot be fertilized.
Why are frozen oocytes destroyed?
Freezing a cell exposes it to many physicochemical changes that can destroy the cell.
In the case of an oocyte, it becomes more vulnerable to freezing due to its weak cell membrane and low surface volume ratio.
It is a known fact that freezing hardens the oocyte zone or shell, which must be injected into the sperm to achieve fertilization.
In addition, freezing can disrupt mitotic spindles, structures that are essential for the proper distribution of oocyte chromosomes.
Current techniques provide a high percentage of surviving oocytes discovered after cryopreservation, but it is not guaranteed that all frozen eggs will develop normally, be able to survive so that they can fertilize, divide and possibly be implanted in the uterus.
Equipment failure can occur with any technique that requires mechanical support systems.
All cryopreserved oocytes can be damaged or damaged by damage to the storage facility or tank; engineering network failures; or fire, wind, earthquakes, water, and other works of God.
Alternatives to cryopreservation and oocyte storage
Alternatives to oocyte freezing to maintain fertility include the use of donor oocytes or frozen pieces of ovarian tissue followed by transfer to the same person later after treatment for cancer or other diseases.
An alternative to freezing all excess oocytes that have not been fertilized in the new cycle is to remove all excess oocytes or fertilize all oocytes and instead freeze the excess embryos.
These frozen fertilized oocytes or embryos can be discovered and later transferred.