Gene expression profiling will be carried out on ribonucleic acid (RNA) from endometrial tissue. As the main objective of this trial is to determine the gene expression profiles of endometrial tissue before and after controlled ovarian stimulation with Gonal-f®, a minimum of 2 endometrial samples per subject will be collected, 1 at day LH+7 of spontaneous cycle and 1 after the stimulation, on the day of OR.