L26/P-338 Prevalence, concomitance and effect in reproductive success of IVF patients diagnosed with benign uterine disorders deemed suitable for transfer: follow-up after high-quality embryo transfer

Abstract Study question What is the prevalence and comorbidity of benign uterine disorders among IVF patients suitable for embryo transfer, and how does their presence affect reproductive outcomes? Summary answer Patients with benign uterine disorders (51.4% of IVF population) showed a 1.46-fold increased relative risk of endometrial failure, rising to a 2.30-fold with their comorbidity. What is known already Benign uterine pathologies, including endometriosis, adenomyosis and uterine fibroids, are challenging to diagnose, particularly endometriosis and adenomyosis, leading to variable prevalence across population. However, with the emergence of improved non-invasive imaging has increased detection, showing these conditions are common in infertile women. While their association with infertility is widely recognized and some studies reported adverse effects on reproductive outcomes, evidence remains controversial. Importantly, these pathologies are often studied individually, despite their frequent comorbidity, and the combined impact on IVF outcomes has not been systematically evaluated, especially independent of embryonic factors. This represents a critical gap in current reproductive research. Study design, size, duration Prospective observational multicenter study assessing the prevalence and comorbidity of endometriosis, adenomyosis and uterine fibroids, and their impact on reproductive outcomes. We included 255 Caucasian IVF patients undergoing endometrial evaluation from January 2018 to October 2025, and subsequently following high-quality embryo transfers (HQET) defined as Day 5 A-B grade embryos (ASEBIR) with confirmed euploidy by PGT-A or derived from oocytes <35 years old from donors or patients. Mean age was 40.9±4.5 years and BMI 22.9±2.8. Participants/materials, setting, methods Patients diagnosed with at least one benign uterine disorder deemed suitable for transfer (n = 131) were divided in diagnosed with endometriosis (n = 35), adenomyosis (n = 77) or uterine fibroids (n = 70), both isolated or coexisting conditions, and their reproductive outcomes were compared with those without uterine pathologies (n = 117). Primary outcomes, implantation (IR) and live birth rates (LBR), and relative risks (RR) with 95% confidence intervals (95%CI), were calculated. Fisher’s exact test was used to assess differences (p < 0.05). Main results and the role of chance At the time of embryo transfer, 131 of 255 patients (51.4%) suffered at least one benign uterine disorder (BUD group), while 117 (45.9%) were not diagnosed during the entire follow-up period and were used as controls. The prevalence found in our population were: isolated endometriosis 13.7% (n = 15), adenomyosis 15.3% (n = 39) and fibroids 14.2% (n = 36), coexisting adenomyosis with fibroids 8.2% (n = 21), endometriosis with adenomyosis 2.7% (n = 7) or with fibroids 1.2% (n = 3), and all of them coexisted in 3.9% of patients (n = 10). BUD patients showed lower IR compared with controls (54.9% vs. 68.4%, p = 0.050) and consequently a 46.5% higher RR of an implantation failure (RR = 1.4646, 95%CI 1.0536-2.0361, p = 0.023). We also found a 28.6% higher RR of not achieving a LB (RR = 1.2856, 95%CI 1.0114-1.6342, p = 0.040), and decreasing trend in LBR (40.5% vs. 53.0%, p = 0.074). Furthermore, when endometriosis, adenomyosis and fibroids were coexisting, the patients also exhibited reduced implantation (27.3% vs. 68.4%, p = 0.0161) with a 130% higher RR of an implantation failure (RR = 2.2998, 95%CI 1.47-3.60, p = 0.0003), and decreased LBR at the limit of significance (18.2% vs. 53.0%, p = 0.054) with 74% increased RR of not achieving a LB (RR = 1.7405, 95%CI 1.2406-2.4418, p = 0.0013). No significant RR was found in adenomyosis and fibroids (isolated or coexisting), neither in endometriosis coexisting with adenomyosis nor fibroids. Limitations, reasons for caution Our study only considered diagnosed pathologies until transfer, and relay on clinical register reported data. For some assessed coexisting conditions, the sample size was limited. Our findings only could be generalizable to IVF Caucasian population undergoing endometrial evaluation. Wider implications of the findings Our findings suggest that benign uterine disorders, even when deemed suitable for transfer, might impair reproductive success. Concomitant endometriosis, adenomyosis, and fibroids, significantly reduce implantation, identifying a high-risk IVF subpopulation for endometrial failure. These results support tailored clinical strategies and further research to optimize implantation outcomes beyond the embryonic factor. Trial registration number No