Immediately after retrieval, the embryologist, an expert in the science of oocyte cryopreservation (the technical term for egg freezing), will rinse, incubate, and prep your eggs for freezing. Before the process of freezing takes place, the embryologist will remove the cells that surround the egg, allowing her to see the egg clearly so she can evaluate the stage of maturation. Only mature, viable eggs are frozen, because these are the only ones that can become correctly fertilized later on. Typically, about 80% of eggs retrieved are deemed mature and suitable for freezing.
After determining which eggs are suitable for freezing, the embryologist will expose each egg to increasingly concentrated levels of cryoprotectants, substances that prevent the formation of ice crystals that can damage the egg. Then, each egg will be placed into a straw, about the diameter of a piece of spaghetti, which has been carefully labeled with your name and unique identification number. All the straws containing your eggs—and only your eggs—are immersed in liquid nitrogen and placed into one larger container, called a goblet, which is also labeled with your name and unique identification number. The goblet is placed inside a storage tank filled with liquid nitrogen, which keeps your eggs preserved indefinitely.
Vitrification is a “flash freezing” technique that cools cells so quickly (to a temperature of -196º Celsius, or about -320º Fahrenheit) that they become “glass-like,” or “vitrified,” minimizing the chance that the water inside the cells will form damaging ice crystals. This is especially important for egg freezing, since eggs (as opposed to other things we might freeze, like sperm) are large size cells with a high content of water. Studies have demonstrated that vitrification is superior to any other method, but not every practitioner offering egg freezing uses it. Here at Extend Fertility, vitrification is the cornerstone of our lab.