Uterine and endometrial factors affecting implantation
Implantation is a process whereby the embryo attaches itself to the luminal surface of the endometrium (inner lining of the uterine cavity). This is followed by migration and invasion of the embryo into the deeper stromal layers (Figure 1). Traditionally, implantation has been considered as a process involving only the embryo and the endometrium, but recent studies show that even cumulus cell competency (cells around the egg) may also contribute to the process. While implantation is a process with a well-defined starting point, it is a gradual process which lasts for several weeks with no universal agreement on when the process is completed.