Biomarkers Related to Endometrial Receptivity and Implantation

Implantation is a process requiring the delicate interaction between the embryo and a receptive endometrium. This intricate interaction requires a harmonized dialogue between embryonic and maternal tissues. [Aghajanova et al., 2008; Simon et al., 2000] The three stages of implantation are: apposition, adhesion, and invasion. Apposition describes trophoblast cells adhering to the receptive endometrial wall. Adhesion to the basal lamina and stromal extracellular matrix occurs in the presence of specific hormones, cytokines, and adhesion molecules. Once the blastocyst is anchored to the endometrial wall, it will become enclosed by an outer layer of syncytiotrophoblast, and an inner layer of cytotrophoblast. As the syncytiotrophoblast erodes the endometrium, the blastocyst will burrow into it and implantation will occur. [Ganong, 2005] During the last few years, research pursues enhancing both the quality of the embryo as well as understanding the highly dynamic tissue of the endometrial wall. Despite morphological and chromosomal criteria to improve the quality of transferred embryos, implantation rates remain at 25-35%. [Boomsma &Macklon, 2006]