Abstract: Recurrent implantation failure (RIF) is an important influence factor of the development of assisted reproductive technologies (ART). At present, the diagnostic criteria for RIF are still not uniform. Based on the literature review, we summarized 12 diagnostic criteria of RIF that published since 2005 and discussed four controversial issues including the number of embryo transfer cycles, the quantity and quality of transferred embryos, the stage of transferred embryos and type of transfer cycles, and the female age. There were differences in the number of embryo transfer cycles (2, 3, 4, 5 and 6 cycles), mainly in the dispute between 2 and 3 cycles, which showed a decreasing trend. There were differences in the number of transferred embryos (3、4、5、8、10 transferred embryos), which also showed a decreasing trend. High quality embryos or blastocysts were selected for transplantation by the morphology or time-lapse photography. The types of transfer cycles include fresh embryo transfer and frozen embryo transfer. The age should be limited due to its effect on the ovarian function and embryo quality. It is generally recognized that the factors of RIF definition include infertile women aged ＜40 years, 3 or more cycles of transplantation (including fresh embryo transplantation and freeze-thaw embryo transplantation), 4 or more high-quality embryos transferred, and no one pregnancy. The inconsistency of diagnostic criteria hinders the progress of RIF treatment. Therefore, it is urgent to carry out the high-quality research and to formulate a standardized RIF diagnostic criterion.

Key words: Recurrent implantation failure, Embryo transfer, Treatment failure, Diagnostic criteria, Review