Received February 11, 2006
Accepted April 08, 2006

Implantation is a phenomenon that involves an interaction between the embryo and maternal endometrium. There is, in the menstrual cycle, a short and precise period of time in which the maternal-embryonic interaction is optimal and culminates with adhesion and invasion of the blastocyst into the progesterone-induced secretory endometrium. This period is called nidation or implantation window. In the implantation window changes occur in endometrial epithelial morphology, characterized by the appearance of membrane projections called pinopodes. The embryonic and maternal expression of growth factors and cytokines, might play a major role in the phenomenon of implantation. Understanding the function of these biomarkers and their role in determining the implantation window in women, will help us to diagnose and treat infertile couples more effi ciently.