In search for an ideal marker of endometrial receptivity: from histology to comprehensive molecular genetics-based approaches

Background: Despite significant improvements in the efficiency of assisted reproductive technologies (ART) for the past 10 years, proportion of unsuccessful cycles still remains significant and can reach up to 40%. Impairment of embryonic implantation is considered as one of the possible causes for low ART efficiency. Implantation failure may be a consequence of a shift in the “window of implantation”, i.e. the period of a cycle when endometrium is most receptive and ready for embryo implantation. Several methods have been developed to evaluate endometrial receptivity, but their accuracy and efficiency are quite different.Aim: Review and efficiency evaluation of the methods used for endometrial receptivity assessment and the window of implantation determination.Methods: We performed a comprehensive literature search (September 2018) with the key words “endometrial receptivity”, “endometrial receptivity evaluation”, “implantation window”, “window of implantation”, “pinopodes” from PubMed and E-library (Russian) databases. One hundred and thirty four (134) publications were selected for the analysis, including 101 original papers and 33 literature reviews.Results: The methods of conventional histology, scanning electronic microscopy, immunohistochemistry, as well as techniques based on the measurement of prostaglandin levels in endometrial fluid and mRNA profiling in an endometrium biopsy sample to assess endometrial receptivity are reviewed. The issue of a search for an ideal endometrial receptivity marker is discussed.Conclusion: At present, the most efficient and accurate methods to diagnose the window of implantation are those based on the mRNA profile assessment of an endometrial tissue sample. Аnalysis of mRNAs allows not only the accurate diagnosis of endometrial receptivity at the time of biopsy to be determined, but also the window of implantation shift to earlier or later periods to be reliably predicted