Natural cycle versus hormone replacement therapy cycle in frozen-thawed embryo transfer.

To compare implantation rates, clinical pregnancy rates and live birth rates associated with natural and hormone replacement therapy (HRT) methods of endometrial preparation in frozen-thawed embryo transfer (FET) cycles.  Methods: The results of 108 natural cycles and 224 HRT cycles of FET transfers performed in a private in vitro fertilization (IVF) center between June 2013 and August 2015 were  retrospectively compared with respect to implantation rate, clinical pregnancy rate, and live birth rate. Results: A total of 144 embryos were transferred in 108 natural cycles and 357 embryos were  transferred in 224 HRT cycles. No statistically significant differences were found in the implantation rate (p=0.796), clinical pregnancy rate per cycle (p=0.900), clinical pregnancy rate per transferred embryo (p=0.283), live birth rate per cycle (p=0.821), or live birth rate per transferred embryo (p=0.481) between the 2 groups.  Conclusion: This study showed no difference between the implantation rate, clinical pregnancy rate or live birth rate between the natural cycle group and HRT cycle group. These results may provide clinicians with more freedom to individualize patient treatment, particularly with respect to the selection of the endometrial preparation method, if these results are supported by large randomized controlled studies in the future.