Mature eggs are the largest cells in the body, containing a large amount of cytoplasm, with a relatively long dehydration time, a low ratio of egg surface area to volume, which is not conducive to uniform cooling or warming of the cell surface and interior, and a slow rate of water entering and leaving the egg. The structure and organelles of the egg are extremely sensitive to changes in temperature and physicochemical factors, and freezing damage is mostly irreversible. Therefore, eggs are inevitably damaged during cryothawing by solute effects, intracellular icing, dehydration, cryoprotectant toxicity, and osmotic pressure effects. The zona pellucida is a transparent non-cellular structure that surrounds the egg periphery and is mainly composed of acidic glycoproteins. The zona pellucida contains sperm receptor proteins, which play an important role in sperm-egg recognition and inducing sperm acrosome response. After sperm entry into the egg, the zona pellucida undergoes biochemical modifications that are involved in preventing multiple sperm fertilization. Egg cryopreservation As the zona pellucida is the structure of the egg exposed to the extra-solutional environment, the structure and function of the zona pellucida are inevitably affected by cryoprotectant toxicity and the chemical and physical effects of the freeze-thawing process acting directly on the zona pellucida. Stiffening of the zona pellucida, the appearance of fissures and ruptures, and changes in the spatial structure of the zona pellucida sperm receptor proteins will affect the zona pellucida function. The meiotic spindle is a dynamic multifaceted structure in the egg, consisting mainly of microtubules. The spindle plays a key role in the completion of meiosis, chromosome arrangement and segregation, dipole formation, and prokaryotic proximity migration after fertilization. The spindle is extremely sensitive to temperature changes, and a drop of 7 degrees below normal body temperature can cause spindle shortening, depolymerization, separation, multipolar spindle, and loss of spindle polarity. Effects on the oolemma The oolemma controls the transport of materials and information inside and outside the egg, and maintains the relative stability of the internal environment of the egg. During fertilization, the membranes are involved in sperm-egg interactions. Therefore, the structural and functional integrity of the membranes is essential for the survival and functional activity of the egg. The damage to the egg membrane during freezing and thawing and rewarming includes rupture of the egg membrane, membrane swelling, changes in the microvilli on the egg membrane, changes in membrane permeability, and degeneration of membrane lipoproteins. After fertilization of frozen eggs, if the meiotic spindle is damaged, the normal segregation of chromosomes may be inhibited, resulting in chromosomal aneuploidy, polyploidy or abnormal prokaryotic formation. Effects on mitochondria Mitochondria are important membrane-phase organelles in the egg that provide energy for the functional activities of the egg through the oxidative phosphorylation pathway. Oxidative phosphorylation is accomplished by enzymes and coenzymes distributed on the inner mitochondrial membrane and cristae. The freezing and thawing process can alter the ultrastructure of human egg mitochondria, resulting in reduced or defective mitochondrial function, decreased ATP production, and failure of the egg to maintain normal functional activity. Microfilaments are fibrous filaments in the egg, the main component of which is fibrillar actin in the polymerized state. They are dynamic and polar structures that together with microtubules form the cytoskeleton and participate in various intracellular motions such as pole body discharge and prokaryotic migration. In summary, it is clear that eggs are inevitably damaged during the freezing and thawing process and that the survival rate, fertilization rate and embryo development rate of human eggs after cryopreservation are low. Therefore, egg freezing is only an option in two special cases (married women treated for malignant tumors to preserve their fertility, and married women who have difficulty in fertilizing their eggs on the day of egg retrieval), and egg freezing is not a fertility insurance policy for women.