How does egg freezing work?
Although sperm and embryos have proved easy to freeze, the egg is the largest cell in the human body and contains a large amount of water. When frozen, ice crystals form that can destroy the cell. Over the years we have learned that we must dehydrate the egg and replace the water with an “anti-freeze” prior to freezing in order to prevent ice crystal formation. We also learned that because the shell of the egg hardens when frozen, sperm must be injected with a needle to fertilize the egg using a standard technique known as ICSI (Intracytoplasmic Sperm Injection). Eggs are frozen using either a slow-freeze method or a flash-freezing process known as vitrification. At USC Fertility we use the slow-freeze method since it is the most studied method and most similar to current embryo freezing techniques. The slow-freeze method may also be safer than the vitrification used by other practices which requires the eggs to be plunged directly into tanks of liquid nitrogen that may harbor viruses.
