The purpose of this study is to determine the differences that exist in RNA molecules, the biochemical process of methylation, and estrogen receptor binding in patients that have failed to produce adequate endometrium in synthetic embryo transfer cycles when compared to patients whose endometrium thickness is within normal limits.

The purpose of this study is to determine the differences that may exist in RNA molecules, the biochemical process of methylation, and estrogen receptor binding (this is a group of proteins in the cell that are activated by the hormone estrogen) in patients that have failed to produce adequate endometrium (uterine lining) in synthetic embryo transfer cycles when compared to patients whose endometrium thickness is within normal limits. Appropriate embryo development and luteal phase (when fertilization and implantation occur) transformation of the endometrium create a small window of opportunity where successful implantation can occur. The interaction between the embryo and the endometrium is complex and poorly understood. The endometrium, which consists of two layers called the functionalis and basalis, goes through changes during the menstrual cycle. The changes that occur are needed for successful implantation of an embryo. The proliferative phase of the menstrual cycle is primarily governed by estrogen and is responsible for the thickening of the endometrium. Progesterone primarily controls the last half of the menstrual cycle and causes changes which allows for embryo implantation. Through in vitro fertilization (IVF), the investigators have seen that the correct thickness of endometrium is a marker of successful implantation and ongoing pregnancy, although the reason for this is not entirely clear. In order to better understand the processes that may occur in the endometrium, the investigators are conducting a study which evaluates biochemical markers of those patients who have shown a failure to proliferate during previous synthetic IVF frozen cycles and biochemical markers of control patients who have no known endometrial pathology.