Embryo freezing is a technique used regularly to optimize the pregnancy rate in case of infertility. This method is performed in presence of supernumerary embryo(s) 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.

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 embryo(s) 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.

Inclusion Criteria:

• Affiliation to the general social security regime and benefiting from 100% infertility;
• Regular Cycles 26 to 35 days;
• Support in IVF or ICSI ;
• Existence of at least 2 frozen embryos to J2 or J3;
• Treated for their first or second cycle of TEC.

Exclusion Criteria:

• Donor sperm;
• Irregular cycles and / or polycystic ovary syndrome;
• Embryos frozen at J1 or J5 / J6 or double planned transfer or transfer of 3 embryos intended;
• Patients who have had more than 3 transfers or more than 6 embryos replaced without pregnancy or puncture rank> 3;
• uterine malformation existing;
• Presence of a hydrosalpinx.