Embryo implantation: Biology, evaluation, and enhancement

PURPOSE OF REVIEW: Implantation is an essential step in the development of a pregnancy, but often fails in humans. In assisted reproductive technologies, implantation failure continues to impair treatment outcomes, with distressing results for patients and physicians. RECENT FINDINGS: Morphokinetics, comprehensive chromosome screening, and the analysis of embryo-derived products detectable in spent culture media offer new means of assessing embryo viability. However, all await validation in randomized controlled trials. Genomic, transcriptomic, and secretomic technologies are similarly being exploited to define specific biomarkers of endometrial receptivity with the aim of identifying novel therapeutic interventions. However, to date no single, clinically relevant molecular marker capable of indicating endometrial receptivity has been reported. Recent work continues to describe the key signalling pathways which result in acceptance or rejection of the implanting embryo. In-vitro studies have revealed that the decidualized endometrium plays an important role in natural embryo selection, which could change our understanding of the aetiology and treatment of reproductive failure. SUMMARY: Recent developments in analytical techniques have initiated a search for biomarkers of embryo quality and endometrial receptivity, and in-vitro studies have revealed novel roles for the decidualized endometrium as a biosensor of embryo quality.