L26/O-096 Progesterone luteal-phase support (LPS) in modified natural cycle frozen embryo transfer (mNC-FET) among women of advanced reproductive age or low ovarian reserve

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Abstract Study question Does progesterone LPS improve reproductive outcomes in mNC-FET among women of advanced reproductive age or low anti-Müllerian hormone (AMH)? Summary answer Women of advanced reproductive age and women with a low AMH did not benefit from vaginal progesterone LPS administered during mNC-FET treatment. What is known already Recent evidence does not support routine use of progesterone LPS in mNC-FET, where human chorionic gonadotropin (hCG) trigger secures ovulation, corpus luteum formation and endogenous progesterone synthesis. However, progesterone LPS could prove beneficial in selected subgroups. Identifying these subgroups is therefore essential to optimise treatment outcomes, support personalised care, and minimise unnecessary interventions. Women of advanced reproductive age and women with a low AMH generally have poorer treatment outcomes, and it is therefore clinically relevant to explore whether LPS influences live birth rates (LBR) in mNC-FET in these subgroups. Study design, size, duration This is a substudy of a completed Danish multicentre, randomised controlled trial (RCT) investigating the effect of progesterone LPS on LBR in mNC-FET. Data from 601 women included in the as-treated population were analysed in this substudy, with participants grouped according to progesterone LPS or no LPS. Data were collected between January 2019 and February 2024. Participants/materials, setting, methods Women aged 18-41 years with regular menstrual cycles undergoing mNC-FET with a single, autologous good-quality blastocyst were included from eight public fertility clinics in Denmark. Risk Differences (RD) with 95% Confidence Intervals (CI) were calculated for associations between progesterone LPS and reproductive outcomes stratified by age (<37 years vs. ≥37 years) and AMH (≥6.29 pmol/L vs. <6.29 pmol/L). Effect modification by age and AMH as continuous variables was examined using logistic regression with interaction terms. Main results and the role of chance LBR did not differ with progesterone LPS use in either age group. Among women aged <37 years (n = 456), live birth occurred in 35.7% with LPS compared to 36.3% without LPS (RD –0.6%, 95% CI: –13.0 to 11.7; p = 0.922). Among women aged ≥37 years (n = 145), live birth occurred in 29.2% with LPS compared to 21.9% without LPS (RD 7.2%, 95% CI: –12.7 to 26.5; p = 0.346). Pregnancy loss rates (PLR) did not differ with LPS in either age group (<37 years: RD –0.7%, 95% CI: –10.1 to 8.7; p = 0.897; ≥37 years: RD –3.8%, 95% CI: –22.2 to 15.0; p = 0.686). Among women with AMH ≥6.29 pmol/L (n = 504), live birth occurred in 34.7% with LPS and 31.6% without LPS (RD 3.1%, 95% CI: –8.5 to 14.5; p = 0.508), with similar PLR (RD –2.3%, 95% CI: –11.6 to 7.2; p = 0.560). In women with AMH <6.29 pmol/L (n = 47), LBR was numerically lower with LPS than without LPS (20.7% vs. 44.4%; RD –23.8%, 95% CI: –56.4 to 13.8; p = 0.108), and PLR higher (RD 9.6%, 95% CI: –23.0 to 35.3; p = 0.692), however both insignificant. No interaction was observed between age and effect of LPS on live birth (p = 0.497), nor between AMH and effect of LPS on live birth (p = 0.133). Limitations, reasons for caution The RCT study protocol did not predefine the primary endpoints of this substudy, and the substudy lacked statistical power. Owing to few events in some subgroups, adjusted risk differences could not be estimated. Age at time of oocyte aspiration and blastocyst vitrification was not available. Wider implications of the findings Progesterone LPS did not increase live birth or reduce pregnancy loss across age or AMH groups and should not be used routinely. Trial registration number Yes

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