Egg freezing takes the eggs of a healthy mother and freezes them to prevent them from aging with the body, and then removes the frozen eggs for use when you want to have children. The eggs are then removed and thawed when the mother wishes to have children, and are fertilized to form embryos for transfer into the uterus. There are two main types of egg freezing, as follows: 1) programmed freezing: the early method of freezing eggs is commonly used, i.e. slow cooling with the help of a programmed freezer under low temperature and low concentration of protective agent; 2) vitrification freezing: the oocytes are rapidly cooled down using a high concentration of cryoprotectant. The liquid in the cytoplasm directly forms a non-crystalline state of vitrified material and is placed in liquid nitrogen for preservation, which is among the commonly used ways of freezing eggs at present.