Effervescent Progesterone Vaginal Tablet Mono-Administration Demonstrated Comparable Pregnancy Rate Across the Different Serum Progesterone Levels on the Day of Embryo Transfer in SHIFT Study

Background: Hormone replacement (HR)-frozen thawed embryo transfer (FET) is preferentially used in Japan. HR-FET needs supplementation of progesterone, but there are few data about the efficacy and safety of vaginal progesterone tablet. The aim of this study is to investigate the efficacy of vaginal progesterone tablet in HR-FET cycle in Japanese patients. Methods: This study was multicenter, single arm, prospective study. Patients with infertility were administered 300 mg/day of vaginal progesterone tablet for luteal phase support in HR-FET cycle from 2015 to 2016. Results: Main outcomes were available for 344 patients, of which 49 in the cleavage stage ET group and 295 in the blastocyst ET group. Ongoing pregnancy rate were 10.2% in cleavage stage ET group and 28.1% in blastocyst ET group. As for the secondary outcomes in the blastocyst ET group, embryo quality of blastocyst, the number of past ET, and maternal age were significantly associated with pregnancy rate at 2 weeks after progesterone administration. Mean serum progesterone level was 12.1 ± 5.3 ng/mL at the day of ET. There was no relationship between the serum progesterone level on ET day and either of pregnancy rates at 2, 4, and 6 weeks after progesterone administration. Conclusions: The efficacy of monotherapy using 300 mg/day of vaginal progesterone tablet in HR-FET was shown and the serum progesterone level on ET day did not affect pregnancy rate. (UMIN000021983)