<qa>  What is the average number of visits with SO?For infertile couples supported by in vitro fertilization, embryo freezing is a technique used regularly to optimize the pregnancy rate per retrieval of oocytes. This method is performed in case of supernumerary embryos after fresh embryo transfer, or freeze all of the embryonic cohort in case of medical reasons preventing the transfer. The embryo or embryos can then be thawed and transferred FET to achieve a live birth. However, it is necessary to first ensure that the transfer is carried out at a time 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 performed by hormone replacement therapy HRT or moderate ovarian stimulation SO. The implantation window can also be assessed by the monitoring of a natural cycle NC. The choice of the key moment for the transfer is determined by ovulation and or the rise of progesterone. To date, no study has demonstrated the superiority of one protocol over another in terms of birth rates. In the investigative center, treatment is usually carried out by daily subcutaneous injections of gonadotrophins followed by ovulation induction. In this context, the implementation of the FET in natural cycle may appear less burdensome for the patient and more physiological. The consideration is additional constraints, NC imposing more frequent monitoring ultrasound and or hormone assays to detect the ovulation peak and less freedom in choosing the date of transfer. The average number of visits with SO is 2.6 per cycle. The aim of this study is to compare the stresses and safety of these two therapeutic proposals to determine the least restrictive for patients. 