L26/P-341 Beyond the eggs : A large-scale multi centric analysis to evaluate the impact of endometriosis on clinical pregnancy rates(implantation factor) in IVF with donor oocytes

Abstract Study question Does endometriosis affect clinical pregnancy rates and implantation independent of oocyte quality in donor oocyte IVF cycles? Summary answer Yes, endometriosis is associated with lower clinical pregnancy rates, independent of oocyte quality, with worsening outcomes as disease stage advances. What is known already Endometriosis is a common cause of infertility, but its impact on oocyte quality vs implantation remains debated. Studies using donor oocytes to isolate uterine factors have been limited by small sample sizes and inconsistent findings. A recent meta-analysis highlighted the need for larger, well-controlled studies to clarify whether endometriosis intrinsically compromises endometrial function independent of oocyte quality. Study design, size, duration This retrospective multicentre cohort study analysed 6,148 first donor oocyte IVF cycles from 82 tertiary ART centres (July 2019–June 2024). It compared 2,587 women with surgically/radiologically confirmed endometriosis to 3,561 controls without endometriosis. Participants/materials, setting, methods Participants were matched for age, BMI, embryo quality, and endometrial preparation protocol. All underwent hormone replacement therapy (HRT) cycles with blastocyst transfer. Primary outcome was clinical pregnancy rates. Secondary outcomes included implantation rates and miscarriage rates. Analyses used multilevel logistic regression, adjusted for clustering and confounders. Main results and the role of chance Implantation rate was significantly lower in the endometriosis group (42.95%) vs controls (49.45%) (adjusted odds ratio [OR] 0.81, 95% confidence interval [CI] 0.73–0.89). Pregnancy (65.56% vs 70.68%) and clinical pregnancy rates (58.52% vs 63.97%) were also lower (all P < 0.05). Miscarriage rate did not differ significantly. A dose-response relationship was observed: implantation rates declined from 44.32% (Stage I) to 36.45% (Stage IV) (P < 0.001). Sensitivity analysis excluding patients with adenomyosis confirmed the association (OR 0.83, 95% CI 0.74–0.93). Results are unlikely due to chance given the large sample and robust matching. Limitations, reasons for caution Retrospective design limits causal inference. Unmeasured confounders (e.g., endometriosis phenotype, prior treatments) may persist. Adenomyosis data were not fully available, though sensitivity analysis addressed this. Findings are specific to HRT cycles and may not generalize to natural cycles. Wider implications of the findings This study provides strong evidence that endometriosis directly impairs endometrial receptivity. Clinical management should include tailored endometrial preparation, especially in advanced stages. Future research should explore possible mechanisms and targeted interventions, such as prolonged GnRH agonist pretreatment or personalised embryo transfer, to improve outcomes. Trial registration number No