Effect of vaginal estrogen supplementation for luteal phase support in the GnRH antagonist protocol on pregnancy outcomes for IVF/ICSI cycles: a randomized controlled trial.

study questionDoes adding vaginal estradiol to standard progesterone luteal phase support improve ongoing pregnancy rates in normal-responder IVF/ICSI patients undergoing GnRH antagonist cycles? SUMMARY ANSWER: The addition of vaginal estradiol to progesterone luteal support in GnRH antagonist cycles, compared to progesterone alone, enhances embryo implantation and clinical pregnancy rates in normal-responder IVF/ICSI patients, yet fails to significantly improve ongoing pregnancy or live birth outcomes. WHAT IS KNOWN ALREADY: The GnRH antagonist protocol for IVF, while advantageous in some aspects, may negatively impact estrogen levels and endometrial receptivity, potentially lowering fresh embryo transfer pregnancy rates compared to agonist protocols. The role of adding estrogen to standard progesterone luteal phase support in antagonist cycles remains controversial, with existing studies yielding conflicting results and a lack of robust randomized controlled trials (RCTs) specifically investigating vaginal estrogen administration. STUDY DESIGN SIZE DURATION: In this single-centre RCT, participants were randomized 1:1 on the ovulation trigger day to receive either progesterone alone (P group) or progesterone plus vaginal 17β-estradiol (E + P group) for luteal phase support, starting on Day 1 post-oocyte retrieval. The sample size calculation, based on detecting a clinically significant 13% difference in ongoing pregnancy rate (43% vs 30%; α = 0.05, power = 80%) with an anticipated 10% attrition, determined a target of 236 women per group. A total of 518 women (P group: n = 259; E + P group: n = 259) were enrolled between April 2019 and June 2022. Allocation used computerized randomization by an independent data manager. Blinding of participants and physicians was not feasible; however, statisticians were blinded until analysis completion. The analysis was performed using intention-to-treat (ITT) and per-protocol (PP), followed by a sensitivity analysis using multivariable logistic regression. PARTICIPANTS/MATERIALS SETTING

methodsThis single-centre trial enrolled 518 infertile women (20-39 years) undergoing fresh IVF/ICSI cycles as normal responders at a tertiary care centre. Participants were allocated to either the P group or E + P group. Luteal support initiated on Day 1 post-oocyte retrieval comprised: vaginal progesterone 90 mg/day + oral dydrogesterone 10 mg twice daily for both groups, with the E + P group additionally receiving vaginal 17β-estradiol 2 mg nightly. The primary outcome was ongoing pregnancy rate, with secondary outcomes including the rates of implantation, clinical pregnancy, live birth, and maternal complications. MAIN RESULTS AND THE ROLE OF CHANCE: The ITT analysis showed no significant differences in ongoing pregnancy rates of 46.33% (120/259) in the E + P group versus 39.00% (101/259) in the P group (RR 1.19, 95% CI: 0.97-1.45; LIMITATIONS REASONS FOR CAUTION: The increase in ICP in the estradiol group is a major safety concern requiring cautious interpretation, despite the improvement in some intermediate outcomes, such as implantation and clinical pregnancy. The lack of significant benefit on the primary outcome, ongoing pregnancy, and live birth limits the clinical utility. WIDER IMPLICATIONS OF THE

findingsThe addition of vaginal luteal estradiol supplementation in GnRH antagonist cycles improves embryo implantation and clinical pregnancy rates, yet fails to demonstrate significant benefits in ongoing pregnancy or live birth outcomes for IVF/ICSI patients. This intervention was associated with an increased risk of ICP compared to that in progesterone-only controls, highlighting the need for clinical vigilance regarding maternal safety. Although there was no significant between-group difference in the incidence of ICP in the sensitivity analysis, this null finding is likely due to the small number of events and limited statistical power. Notably, ICP should remain a safety signal that warrants attention when estrogen supplementation is administered during early pregnancy. These findings indicate that while estradiol supplementation may enhance early reproductive endpoints, its clinical utility remains uncertain due to the absence of ultimate efficacy improvement and emerging safety concerns. STUDY FUNDING/COMPETING INTERESTS: The grant support was provided by: the Key R&D Program of Zhejiang (2024C03199), Zhejiang Provincial Medical and Health Technology Plan (2020KY620, 2025KY1176), Zhejiang Provincial Natural Science Foundation of China (LQ24H040002, LHZQN26H280003), Administration of Traditional Chinese Medicine of Zhejiang Province, China (2024ZL740), and Hangzhou Municipal Special Fund for the Development of the Biomedicine and Health Industry (2023WJC327). There are no conflicts of interest to declare. TRIAL REGISTRATION NUMBER: ChiCTR1900022631. TRIAL REGISTRATION DATE: 19 April 2019. DATE OF FIRST PATIENT’S ENROLMENT: 20 April 2019.