General cryopreservation of eggs utilizes liquid nitrogen at -196°C. Any cells at such a low temperature are biologically inactive. Therefore, in theory, they can be preserved indefinitely, for 10, 20, 30 or even hundreds of years. The current technology of cryopreservation, there is open preservation and closed preservation, which means that the eggs are not whether they are in direct contact with liquid nitrogen. It has been found that there is no limit to the number of eggs that can be preserved. Direct contact with liquid nitrogen may cause damage to the DNA of the eggs, so generally speaking, closed preservation is the best option. Currently, worldwide, cryopreserved eggs have been kept in liquid nitrogen for five or ten years without any abnormalities, so eggs can be preserved for more than ten years.