With the increasing maturity of IVF technology, the success rate has been improving year by year, the clinical pregnancy rate of each transplantation cycle has exceeded 50%, and the prognosis of patients with good prognosis (young patients with normal ovarian function in the first IVF) can even reach 70-80%. However, there are still some patients who still cannot get pregnant after three or more IVF cycles, which is called “repeated IVF failure” in medicine. “Repeated IVF failure” is one of the most prominent problems in the field of assisted reproductive technology, including cycle cancellation due to poor ovarian response, low ovarian response, fertilization failure, implantation failure and repeated miscarriage. Repeated implantation failure is one kind of repeated IVF failure. Currently, there is no standardized definition, but in the past, repeated IVF treatment for more than 3 transfers; or cumulative transfer of more than 10 highly rated embryos failed to conceive is considered as repeated implantation failure. In recent years, with the improvement of embryo culture techniques and the popularity of blastocyst culture and single embryo transfer, it is clear that the past criteria are no longer applicable. It is now considered that repeated implantation failure is diagnosed when a total of 4-6 highly rated embryos or 2-3 blastocysts are transferred and still fail to conceive. Repeated implantation failure may be due to poor embryo development potential, decreased endometrial receptivity, or abnormalities in the dialog between the embryo and the endometrium. But what exactly is the cause in a particular patient? Doctors often have difficulty determining, and patients are both confused and distressed. What aspects should be considered and dealt with this thorny issue? I. Embryonic factors The existence of ectopic pregnancy and scarred pregnancy suggests that embryo quality is the most critical factor in embryo implantation. The current evaluation indexes of embryo quality in IVF clinic are as follows: 1. Embryo morphology score: the most widely used evaluation standard of embryo quality, although convenient and practical, it can not really reflect the quality of embryo and its ability to implant comprehensively. Those who have failed to conceive after multiple transfers of high scoring cleavage stage embryos can be further screened by blastocyst culture. Patients with recurrent poor morphological scores can try microstimulation or natural cycling to reduce the dose of exogenous ovulation stimulating drugs with a view to improving egg and embryo quality. 2. Embryo growth rate and timing: The dynamic observation microscope system (Time Lapse) allows continuous observation of the embryo for 24 hours during its development, so that its growth rate and timing of division can be evaluated and the most normal embryos can be selected for transfer. Patients with recurrent poor morphologic scores can also be observed by Time Lapse to characterize the process of embryo division and fragmentation. 3, embryo chromosome abnormality: embryo chromosome aneuploidy is one of the reasons for embryo implantation failure. For some patients with advanced age, repeated implantation failure and repeated spontaneous abortion, preimplantation genetic screening (PGS) can also be considered for screening. Second, uterine factors 1, uterine factors: just as planting needs fertile soil, implantation also needs a suitable endometrium. When there are uterine abnormalities, such as polyps, submucosal fibroids, uterine adhesions, endometritis and other pathologies, may reduce the chances of implantation. There is clear evidence that hysteroscopy can identify and resolve the etiology and significantly improve the implantation rate in some patients with recurrent failure. For patients with repeated failures who have normal uterine cavity morphology, endometrial scratching can also be performed during the luteal phase to improve the acceptability of the endometrium. 2, tubal effusion: tubal effusion contains various “poisons”, if left untreated, reflux to the uterine cavity, will “wash away” “drown” “poison” the embryo. If left untreated, reflux into the uterine cavity will “wash away,” “drown,” and “poison” the embryos, thus greatly reducing the chances of embryo implantation. For patients with repeated failures, the first step is to check whether the tubes are combined with hydrosalpinx. If there is hydrosalpinx, it is recommended to deal with the hydrosalpinx first, and ligate or remove the tubes to remove the effect of the fluid on the implantation. If the pelvic adhesions are serious and inoperable, tubal occlusion can also be considered. Third, immune factors 1, immune abnormalities: research suggests that systemic or local natural killer cell activity is abnormally elevated, which may have a toxic effect on the embryo and impede implantation. It can be treated by intravenous infusion of immunoglobulin or fat milk. In addition, active immunodeficiency can be induced by injecting husband lymphocytes, which induce their own active immune function. However, there is controversy about the effectiveness of various treatments for immune abnormalities. Coagulation abnormalities: Coagulation abnormalities, such as “antiphospholipid syndrome” and “thrombophilia”, lead to thrombosis in the small blood vessels of the placenta, resulting in insufficient blood supply to the uterine lining, decreased chances of implantation of the embryo, or increased risk of miscarriage, which can be prevented and treated with aspirin, corticosteroid, and low molecular heparin. It can be prevented and treated by aspirin, corticosteroid, low molecular heparin and so on. Psychological factors Excessive psychological stress may lead to endocrine disorders, which may also cause uterine muscle contraction disorders. Studies have shown that the IVF pregnancy rate of patients with excessive psychological stress is significantly lower than that of other patients. Therefore, relaxation, improvement of lifestyle, appropriate exercise, more communication with family members, and seeking psychological support and help are also very beneficial to the success of IVF. In conclusion, the etiology of repeated IVF failures is complex, and it is the mission of clinical IVF doctors to analyze the causes and find countermeasures to improve the implantation rate and pregnancy outcome according to the specific conditions of patients. It is the mission of clinical IVF doctors to analyze the causes of IVF failure, find countermeasures to improve the implantation rate and pregnancy outcome!