 Do differences in endometrial gene expression exist after different protocols of endometrial preparation for embryo transfer? The clinical results in different publications showed different results, some of them described the natural cycle superior as the substituted cycles, and in contrast other large series showed superior results in substituted cycles than natural but with an increased of pregnancies losses. The recent apparition of endometrial receptive arrays technology let us know if endometrial is receptive or not in patients with some problems of infertility as implantation failure, for that we want to know if this technology would tell us if the different kind of protocols for endometrial preparation origin differences that could explain some of the founded results. 