Prospective Randomized Non-Inferiority Study Comparing Natural Cycle Frozen Embryo Transfer (NC-FET) to a New Type of Endometrial Preparation for FET: Natural Proliferative Phase (NPP-FET)

Frozen embryo replacement cycle :Two methods traditionally used: the spontaneous cycle and the artificial cycle.Now, Emergence of new protocols: NPP-FET or "Natural proliferative phase - frozen embryo transfer" Demonstrate non-inferiority between the NPP-FET and the spontaneous cycle, and superiority in terms of planning.