What exactly do we mean by 'recurrent implantation failure'? A systematic review and opinion.

Recurrent implantation failure (RIF) is an iatrogenic condition, being the result of repetitive unsuccessful cycles of IVF or intracytoplasmic sperm injection (ICSI) treatment. The aim of this review was to assess the definitions of RIF used in literature as well as suggest a uniform definition of this condition. A systematic search of MEDLINE, Embase and Cochrane Library was conducted. The most commonly stated definitions described RIF as 'three or more failed treatment cycles' or 'two or more failed cycles'. Other identified definitions were based solely on the number of embryos transferred in previous cycles or combined the number of previously failed cycles with the number of transferred embryos. Several other definitions were also identified. This review highlights the lack of uniformity of the definition of RIF. Based on the available literature and the expert opinion of the authors, RIF should be defined as the absence of implantation after two consecutive cycles of IVF, ICSI or frozen embryo replacement cycles where the cumulative number of transferred embryos was no less than four for cleavage-stage embryos and no less than two for blastocysts, with all embryos being of good quality and of appropriate developmental stage.