Molecular Biomarkers of Endometrial Function and Receptivity in Natural and Stimulated Assisted Reproductive Technology (ART) Cycles

The success of embryo implantation and pregnancy depends on a complex interaction between the trophoblast and the endometrial environment, where endometrial receptivity plays a crucial role in this process. Assisted reproductive technologies (ARTs) are essential in overcoming biological barriers and enabling implantation in women with fertility issues. However, one of the main challenges in ART is ensuring that the endometrium is receptive at the time of implantation. Therefore, identifying endometrial receptivity biomarkers is essential to optimize ART treatments, improving success rates. A comprehensive literature review was conducted by searching peer-reviewed articles published in PubMed, Scopus, and Web of Science databases. The search included studies focusing on molecular and cellular mechanisms underlying endometrial receptivity in both natural and stimulated cycles. Various experimental methods, including proteomic and microRNA studies, have identified key biomarkers involved in endometrial receptivity, such as adhesion molecules, growth factors, and others. However, ovarian stimulation in fertility treatments can alter endometrial receptivity, making approaches like frozen embryo transfer necessary. Despite advancements, many questions persist regarding the endometrial receptivity and implantation mechanisms in both natural and stimulated cycles. This article reviews the main molecules involved in endometrial receptivity in natural and stimulated cycles, highlighting their potential role as biomarkers for embryo implantation.