Comparing the success rate of natural cycle and modified natural cycle protocols for frozen-thawed embryo transfer.

: The aim of the present study is to compare the effects of Natural Cycle and modified Natural Cycle protocols for frozen-thawed embryo transfer on clinical pregnancy rate and live birth rate. This prospective randomized controlled trial comprised 145 patients scheduled for frozen-thawed embryo transfer and was conducted at a university hospital between 2019 and 2021. The Natural Cycle protocol was administered to 73 patients and the modified Natural Cycle protocol to 72 patients and the clinical outcome was compared between the groups. The main outcome measure was live birth rate. Baseline characteristics and cycle parameters were similar in both groups. There was no difference in clinical pregnancy rate (58.9% and 54.2%, respectively;  = .565) and live birth rate between the Natural Cycle and modified Natural Cycle groups (49.3% and 48.6% respectively;  = .932). This study established that clinical pregnancy and live birth rates were not affected by natural cycle ovulation being spontaneous or hCG-triggered among patients undergoing frozen-thawed embryo transfer. Thus, the protocol for natural cycle frozen-thawed embryo transfers should be chosen according to the priorities of the patient and the physician.