Multicenter cohort study of the effect of Crinone® progesterone vaginal gel alone to prepare the endometrium for frozen–thawed blastocyst transfer in a hormone replacement cycle

Aim: Progesterone has to be administered to prepare the endometrium for frozen–thawed blastocyst transfer (FBT) in a hormone replacement cycle (HRC). The objective of this study was to investigate the efficacy and safety of using Crinone® progesterone gel alone in HRC-FBT. Methods: In this multicenter prospective study, HRC-FBT was performed with blastocysts with a Gardner's classification of 3BB or better, and application of 90 mg/day of vaginal gel (Crinone, Merck BioPharma, Tokyo) was started when the endometrial thickness reached 8 mm or more. The primary endpoint was the clinical pregnancy rate (CPR). Safety endpoints included genital bleeding and other adverse events. Recruitment started in May 2018. Results: A total of 181 patients were enrolled, and 156 were included in the efficacy analysis. The overall CPR was 41.7% (65/156). In patients younger than 38 years (n = 113), the CPR was 48.7% (55/113), and in those aged 38 years or older (n = 43), it was 23.3% (10/43). The overall CPR was comparable to that observed in the Japan Society of Obstetrics and Gynecology ART2020 National Survey, which reported a pregnancy rate of 36.3% in frozen embryo transfer cycles. Adverse events such as light genital bleeding occurred before and after pregnancy in some patients, but at a low frequency (<10%). Conclusions: Use of Crinone progesterone vaginal gel alone is adequate in HRC-FBT and is not associated with any safety issues.