Determining diagnostic criteria and cause of recurrent implantation failure

Purpose of review Recurrent implantation failure (RIF) refers to the absence of implantation after repeated transfer of good embryos into a normal uterus. This review discusses the diagnostic criteria and cause of RIF. Recent findings Regardless of the advancements in IVF practice, RIF is still a challenge that has to be solved. Exact definition of RIF is lacking today. For the initial evaluation, a rigorous algorithmic evaluation should be compromised with an individualized principle. Factors that might affect the number and quality of the oocyte and sperm cells should be investigated in order to obtain a good-quality embryo. Embryo assessment should be performed under ideal laboratory circumstances. The uterine environment should be carefully evaluated and the embryo should be transferred into the uterus at the most receptive time. Some of the newly introduced diseases and empirical treatment strategies, such as chronic endometritis, vaginal microbiota, immunologic profile and immunomodulator treatments, can be discussed with the couple under the light of adequate evidence-based information. Summary New diagnostic and treatment modalities are needed to be introduced, which would be safe, efficient and efficacious after well-designed randomized controlled trials.