<qa>  What is the purpose of this open randomized study?Embryo freezing is a technique used regularly to optimize the pregnancy rate in case of infertility. This method is performed in presence of supernumerary embryos after fresh transfer, or after freeze all embryos in case of medical reasons. It is necessary to control that the transfer is performed when the endometrium is receptive, which is essential for embryo implantation and pregnancy. This period is defined as the implantation window. Endometrial preparation can be achieved by hormone replacement therapy HRT or moderate ovarian stimulation SO. The implantation window can also be assessed by monitoring of a natural cycle NC. The objectives of this open randomized study is to compare the number of visits ultrasound and blood tests induced by the SO or NC as well as the women quality of life in both groups. 