Table 1_Recurrent implantation failure: a registry-corroborated, age-stratified definition and pragmatic five-tiered management algorithm.docx

RIF is generally defined as failure to achieve pregnancy after multiple transfers of good-quality embryos, yet progress in the field has been constrained by the absence of a universally accepted definition and by the inherent complexity of investigating the embryo–endometrial interface.

Recent evidence has prompted a reappraisal of the factors contributing to RIF, distinguishing it from the mechanistically distinct entity of embryo-intrinsic failure (recurrent embryo arrest and poor embryo development). This narrative review synthesises epidemiological data, evaluates the evidence base for available diagnostic modalities, and appraises current management strategies, including the controversies surrounding adjunctive treatments.