What is the optimal endometrial preparation protocols in euploid frozen embryo transfer (fet)?

Various factors, including treatment protocols, can influence the outcomes of frozen embryo transfers (FETs). In order to prepare the endometrium, several protocols have been suggested: natural cycles, where detecting the luteinising hormone (LH) surge, and, therefore, the ovulation, defines the timing of the transfer; modified natural cycles, where ovulation is triggered by the administration of human chorionic gonadotrophin (hCG); hormone replacement therapy (HRT) or artificial cycle with estradiol (E2) and progesterone (P4), with or without using gonadotropin-releasing hormone (GnRH) analogs; and, finally, stimulated cycles with low doses of gonadotropins. However, there is still some controversy as to the ideal endometrial preparation protocol. Also, the efficacy and the safety of these FET protocols have been examined by multiple studies, but there is a lack of consensus on how the endometrium should be prepared and synchronized. Is the pregnancy outcomes in euploid frozen embryo transfer (FET) cycles affected by the endometrial preparation protocols?