L26/O-209 Impact of adenomyosis on in vitro fertilisation outcomes in women undergoing frozen embryo transfers: a prospective observational study

Abstract Study question Do adenomyosis characteristics (type, location, severity) and GnRHa pretreatment affect live birth rates after frozen embryo transfer? Summary answer Adenomyosis severity and intrinsic location lower live birth rates. GnRHa pretreatment reduces disease severity and improves pregnancy and live birth outcomes. What is known already Adenomyosis is associated with adverse reproductive outcomes, but the impact of its specific features—such as type, location, and severity—on frozen embryo transfer (FET) success remains unclear. The potential benefit of GnRHa pretreatment before FET in adenomyosis patients is also not well-defined, with existing evidence being inconsistent. Study design, size, duration Ambidirectional observational cohort study conducted at a university-affiliated IVF center from January 2019 to January 2023. It included 1,407 first-FET patients: 415 with adenomyosis and 992 without. Participants/materials, setting, methods Infertile patients underwent FET following natural or artificial endometrial preparation. Adenomyosis was diagnosed and classified via transvaginal ultrasound. Outcomes (live birth, pregnancy, miscarriage rates) were compared between groups, and associations with adenomyosis features/GnRHa pretreatment were analyzed. Main results and the role of chance Compared to controls, adenomyosis patients had a lower live birth rate (37.11% vs. 44.86%; aOR 0.522, 95% CI 0.338–0.806, p = 0.003) and higher miscarriage rate (25.24% vs. 16.82%; aOR 1.772, 95% CI 1.005–3.126, p = 0.048). Among adenomyosis patients, greater disease severity independently reduced chances of biochemical pregnancy, clinical pregnancy, and live birth (all p < 0.001). Anatomical location significantly influenced outcomes; extrinsic and intramural types had superior results to the intrinsic type (all p < 0.001). Diffuse vs. focal type and uterine volume showed no significant associations. GnRHa pretreatment was associated with improved biochemical pregnancy (OR 1.903, p = 0.015), clinical pregnancy (OR 2.379, p = 0.002), and live birth rates (OR 3.099, p < 0.001), and significantly reduced disease severity score (p < 0.001). Limitations, reasons for caution Observational design cannot prove causality. Ultrasound-based diagnosis might miss subtle lesions. Findings from a single center may limit generalizability. Wider implications of the findings Adenomyosis severity and location are key prognostic factors. GnRHa pretreatment appears beneficial, suggesting personalized endometrial preparation protocols could optimize FET outcomes for these patients. Trial registration number No