Natural cycle is superior to hormone replacement therapy cycle for vitrificated-preserved frozen-thawed embryo transfer

We undertook this retrospective variables-control analysis to compare the reproductive outcomes of frozen-thawed embryo transfer using endometrial preparation with either natural cycle or hormone replacement therapy cycle. Patients were divided into three subgroups. Subgroup A (n = 32) consisted of patients having three 8-cell post-thawed embryos transferred. Subgroup B (n = 404) consisted of patients having three good quality post-thawed embryos transferred. Subgroup C (n = 578) consisted of patients having two or three all intact and mitosis resumption post-thawed embryos transferred. Implantation rate, biochemical pregnancy rate, and clinical pregnancy rate were measured. In subgroup A, significantly higher implantation rate, clinical pregnancy rate ongoing pregnancy rate, and lower biochemical pregnancy rate were observed in the natural cycle compared with hormone replacement therapy (HRT) cycle. Subgroup B, had a significantly higher rate of implantation, ongoing pregnancy, and a significantly lower rate of biochemical pregnancy in natural cycle compared with HRT cycle. The natural cycle had a higher trend of clinical pregnancy rate without reaching statistical significance. No statistical difference in reproductive outcomes between natural cycle and HRT cycle was observed in subgroup C. The results suggest the superiority of the natural cycle as compared with the HRT cycle under certain circumstances in a selected population of patients.