With the recent liberalization of the second-child policy, our center has received many calls asking about embryo freezing, and many patients may have had their embryos frozen for three or four years or even longer. How long can embryos be frozen and preserved? The longer the freezing time, the worse the survival rate is? Do frozen embryo babies have more birth defects than regular IVF and natural births? The following are answers to each of these questions, using a large number of statistics from home and abroad. Regardless of the freezing technique, the final embryos will be preserved in liquid nitrogen (-196°C), and in theory, under a stable liquid nitrogen environment and natural radiation, embryos can be preserved for more than 2000 years! In a practical sense, embryos can be preserved in liquid nitrogen for 5-10 years. Studies have proven that cryopreservation time has no effect on embryo survival and implantation rates. One study analyzed 11,768 frozen embryo transfer cycles and found no difference in embryo survival rate, embryo implantation rate, clinical pregnancy rate, miscarriage rate, and live birth rate when comparing embryo cryopreservation for 1-3 months, 3 months-1 year, 1-2 years, 2-3 years, and more than 3 years. In another study comparing embryos preserved for 6 months with those preserved for 2-9 years, there was no difference in embryo survival and implantation rates. A large body of clinical data confirms the safety of frozen embryos, which can be stored stably for 5-10 years, and that the length of cryopreservation does not affect the ability of embryos to continue to develop. As long as the embryos survive after resuscitation, there is little impact on the quality of the embryos. The birth weight and developmental status of babies born with frozen embryos, as well as the physical and IQ development of children later on, are within the normal range.