Human fertilization is a complex series of processes in which sperm enter the egg and the sperm head depolymerizes to form the male pronuclei (malepronuclei), while the egg is activated and undergoes a series of transformations to form the female pronuclei (females). The formation of female pronuclei is generally synchronous, and male and female pronuclei may be observed as early as 6 hours up to 20 hours after insemination, i.e. 2PN, after which the male and female pronuclei approach each other, fuse, the pronuclei disappear and fertilization is complete. Therefore, the observation of double protoplast nuclei indicates successful fertilization, and the fusion of male and female protoplast nuclei is a sign of fertilization completion. In clinical practice, due to working hours and the environment in which the embryos are cultured, most fertility centers only observe the prokaryotic condition 16-20 hours after insemination. If the prokaryotic nucleus is not observed, i.e. 0PN, 0PN may exist in the following situations: 1. Slow development of the prokaryotic nucleus, delayed fertilization, and no prokaryotic nucleus has been formed within the observation time. 2, Prokaryotic development is too fast, the egg has completed fertilization and the prokaryotic nucleus has fused and dissolved within the observation time. In both cases above the egg is actually successfully fertilized and a normal embryo can be obtained eventually. 3. The eggs are not fertilized. Some 0PN can develop oogenesis and blastocyst stage, and their morphology and embryonic development rate are similar to those of normally fertilized embryos of 2PN origin, but it is not certain whether they come from normal fertilization. Figure 1 2PN Figure 2 0PN In clinical work, 2PN-derived embryos are preferentially selected for transfer, but sometimes, especially for older patients with declining ovarian function, sufficient 2PN-derived embryos cannot be obtained, so can 0PN-derived embryos be transferred and is it safe at that time? To investigate the value of 0PN-derived embryos, Ming Li et al. compared the pregnancy outcomes of 0PN embryos at the oogenesis stage, 0PN embryos at the blastocyst stage and the corresponding 2PN embryos. A total of 368 0PN oogenesis/blastocyst stage embryos were included. It was found that the pregnancy rate of 0PN embryos was significantly lower than that of 2PN embryos in oogenesis embryos (fresh cycle: 8.04% vs. 19.50%, frozen cycle: 15.38% vs. 28.24%, P<0.05), while the pregnancy rate of 0PN embryos in blastocyst stage embryos was similar to that of 2PN (39.56% vs. 48.18%, P>0.05). The study concluded that embryo development from oogenesis to blastocyst stage is also a process of selection and elimination, and when the embryo itself has problems, then it is difficult to develop further into blastocyst, and extending the time of in vitro culture can gradually screen out non-diploid embryos and increase the proportion of normal embryos. Ultimately, a total of 44 babies were born from embryos of 0PN origin in this study, all of them healthy, and the 0PN embryos were considered safe. In other studies, Manor, Malcov et al. analyzed 0PN embryos and found that some of the 0PN embryos were normal diploids and were considered safe for embryo transfer. However, there are relatively few studies on 0PN embryos, and the safety of 0PN-derived embryos for transfer still requires large samples and long follow-up. Currently, 0PN-derived embryos at the oogenesis stage in our center will not be transferred, and will continue to be cultured in vitro until the blastocyst stage before being cryopreserved. In the absence of 2PN embryos, 0PN embryos can be transferred with full informed consent of the patient. In addition, the time-lapse embryo observation technique (time-lapse), which has emerged in recent years, can dynamically observe embryo development with a short and fixed image acquisition interval (generally 5-20 min), which not only allows dynamic observation of embryo morphology, but also provides information on the time of embryo morphological changes and ensures the stability of the embryo developmental environment during the observation process, which can It provides clues to the origin of 0PN embryos. At present, our center also has this technology.