The endometrium as a cause of implantation failure.

One of the biggest obstacles to reproductive success is our inability to diagnose or treat effectively the non-receptive endometrium. The endometrium becomes receptive for a limited period of time under the influence of steroid hormones and paracrine signals from the developing embryo. It is likely that the receptive state is characterized by the expression of particular genes that allow the normally refractory endometrium to respond to the embryo and permit attachment. Recently, several molecules have been reported whose function is essential for uterine receptivity in rodents and primates. This article will review current models of the control of receptivity and early implantation and assess progress in defining markers for the receptive endometrium in women. Although some genes have been identified whose expression is altered in women with subfertility, none of these molecular markers have yet proven clinically useful in the assessment of functional receptivity. The use of high throughput techniques such as microarrays and proteomic methods to investigate gene expression in the endometrium provides a novel approach to defining receptivity at the molecular level. The potential impact of these tools on clinical practice will be discussed.