O-205 Dydrogesterone versus micronized vaginal progesterone for luteal phase support in hormone replacement therapy frozen embryo transfer cycles (REMODEL): an exploratory randomized controlled trial

Abstract Study question Is dydrogesterone (DYD) comparable to micronized vaginal progesterone (MVP) for luteal phase support (LPS) in hormone replacement therapy frozen embryo transfer (HRT-FET) cycles? Summary answer Ongoing pregnancy rates (OPR) at 12 weeks’ gestation were comparable between the study group using DYD and the control group using MVP. What is known already Thanks to vitrification, the number of frozen embryo transfer cycles has significantly increased, prompting for a thorough optimization. Few studies have prospectively compared different progesterone regimens in artificial frozen embryo transfer cycles. Currently, MVP is most commonly used for LPS in this setting, but side effects such as vaginal discharge cannot be neglected. Dydrogesterone, a selective progesterone receptor agonist with a high oral bioavailability, could be considered due to its more patient-friendly administration. Two randomized controlled trials confirmed the non-inferiority of dydrogesterone to MVP for LPS in fresh cycles, but robust data on its use in HRT-FET cycles remain limited. Study design, size, duration An exploratory randomized controlled trial was conducted at a university hospital from October 2021 to September 2023. Subjects were randomly allocated 1:1 to the study group using DYD (10mg three times daily) for LPS or the control group using MVP (2x200mg twice daily), all performing FET in a HRT cycle. The primary outcome was ongoing pregnancy rate at 12 weeks (OPR). Secondary objectives included biochemical pregnancy loss, early pregnancy loss (EPL) and live birth rate. Participants/materials, setting, methods Patients under 41 years of age with a normal BMI undergoing a single blastocyst transfer in a HRT-FET cycle without endometrial abnormalities were eligible for inclusion. Patients who required more than 14 days of estradiol valerate priming (2mg three times daily) to achieve an endometrial thickness of at least 7 mm were not included. Of the 170 patients screened, 19 did not meet the randomization criteria and 3 withdrew after randomization. Main results and the role of chance Demographic characteristics such as age, BMI, cause of infertility and regular cycle were comparable between the study and control groups, as were the frozen transfer cycle characteristics. With three drop-outs after randomization, both a per-protocol (PP) and an intention-to-treat (ITT) analysis were performed for the primary outcome. According to the PP analysis, the OPR was 31.5% in the study group and 45.3% in the control group (p = 0.08, difference in proportions (%) -14, 95% CI: -39-11). The ITT analysis showed similar results (OPR 31.1% versus 44.2% in the study and control groups, respectively, p = 0.10). Multivariate regression adjusting for age, BMI, endometrial thickness and parity showed no significant association between the type of LPS administered and OPR (OR 1.92, 95% CI 0.95-3.86, p = 0.07). Positive hCG rates were comparable between both groups (58.9% versus 61.3% in the study and control groups, p = 0.76). Differences in biochemical pregnancy loss (14.0% versus 2.2% in the study and control groups, respectively, p = 0.05) and EPL (32.6% versus 23.9% in the study and control groups, respectively, p = 0.37) did not reach statistical significance. The live birth rate did not differ significantly between the two groups (26.8% versus 41.9%, p = 0.06), but the delivery outcome of 3 patients is missing to date. Limitations, reasons for caution Despite the randomized nature of the study, the exploratory design warrants cautious interpretation of the results due to the primary outcome’s insufficient statistical power. The dosages of the LPS medication used are based on common clinical practice, but due to the absence of dose-finding studies, this may impact the results. Wider implications of the findings The results, although not statistically significant, may raise clinical implications and call for larger studies. A forthcoming analysis will assess progesterone levels throughout the cycle in these study patients, examining their impact on pregnancy outcomes. Given differences in pharmacological profiles, various dosages may also be explored. Trial registration number NCT04758871