Until recently, the only method for freezing oocytes was a slow-freezing method. Unlike sperm, which has been successfully frozen and used for years, eggs contain a great deal of water, which makes freezing more difficult. When the eggs are frozen, ice crystals can form within the egg. These ice crystals can destroy the cell’s structure.
To help minimize the amount of ice crystals, scientists would remove some of the water as the egg was slowly frozen. But it’s impossible to remove all the water, and they couldn’t prevent the formation of some ice crystals. The fertilization and pregnancy Vitrification is a specialized freezing technique, which freezes the egg so quickly, ice crystals don’t have time to form.
Embryo freezing is still the preferred technique for fertility preservative, but this new technique is being used for young or single cancer patients, who don’t want to use a sperm donor. Egg vitrification is still considered to be experimental.