A frequent pitfall found in the literature is the consideration that implantation is the result of good embryonic quality. Although this is completely true, it is not the only truth because the maternal endometrium is at least of equal relevance. In ovum donation, the endometrial factor could also be improved by individualizing the implantation window in each patient. In this proposed research we will analyze suggested markers of endometrial receptivity in order to optimize human implantation in patients undergoing assisted reproductive technologies focusing on improving endometrial receptivity in IVF and ovum donation patients.