This is a Phase IV, pilot, open-label, national, multi-centric study planned to determine the gene expression profiles and histologic changes of the endometrial tissue before and after stimulation with Gonal-f®. Physicians are interested in identifying predictive genetic markers in assisted reproductive technologies (ART) in addition to the clinical predictive factors already known. Among those predictive factors, the state of the endometrium is considered as an important implantation determining factor for which pharmacogenomic research is of great interest.