Personalized embryo transfer (pET) guided by endometrial receptivity (ER) assessment - a possibility to increase effectiveness of in vitro fertilization (IVF) procedures. Review of available methods

The continuous development of assisted reproductive techniques (ART) implies the search for solutions that could increase the effectiveness of available methods. In the context of in vitro fertilization (IVF), a significant proportion of failures are due to unsuccessful embryo transfers. At this stage the most important issue is proper dialogue between implanting embryo and the maternal endometrium. Therefore, it seems justified to assess endometrial receptivity (ER), defined as the tissue's ability to accept an embryo to attach and invade into the mucosa. Window of implantation (WOI), is a certain period in which implantation of the properly developed embryo is possible. The cause of endometrial receptivity disorders is believed to be the disturbed expression of cytokines and endometrial surface proteins, the presence of which has been proven in commonly diagnosed diseases such as endometriosis or chronic endometritis. Despite many years of research on endometrial receptivity, the area of diagnostic methods enabling clinical monitoring of ER still remains undeveloped. The aim of this study is to review the utility of selected markers and the available methods of ER assessment, ranging from noninvasive ultrasound, through endometrial fluid analysis, to genomic studies based on endometrial biopsy, in order to increase the effectiveness of IVF. Such an approach could potentially be a significant step towards personalizing medical procedures especially in patients diagnosed with repeated implantation failure (RIF).