Investigation of endometrial vasculature the day before frozen embryo transfer in internal adenomyosis: a prospective observational study

RESEARCH QUESTION: What is the feasibility of three-dimensional power Doppler ultrasound to predict clinical pregnancy outcome following frozen embryo transfer (FET) in patients with internal adenomyosis (ADM)? DESIGN: This prospective observational study included 61 patients undergoing assisted reproductive technology (ART) who were diagnosed with internal ADM using pelvic magnetic resonance imaging between 10 December 2023 and 1 March 2025. In addition, 116 patients with tubal factor infertility, undergoing ART during the same period, were included as controls. The endometrial blood flow index was measured on ultrasound the day before embryo transfer. The flow index, demographic data and FET outcomes were compared between the two groups. RESULTS: One-way analysis of variance revealed significant differences in the clinical pregnancy rate between the two groups (internal ADM: 20/61, 32.79%; control, 65/116, 56.03%; P = 0.003). The mean ± SD flow index in the internal ADM group (14.74 ± 5.16) was lower than in the control group (17.05 ± 6.65; P = 0.019). Univariate logistic regression analysis revealed that the flow index affected the clinical pregnancy rate significantly, with an OR of 1.126 (95% CI 1.064-1.193; P = 0.001). Multivariable logistic regression of FET outcomes indicated that the flow index affected the clinical pregnancy rate significantly (OR = 1.112, 95% CI 1.049-1.180; P = 0.001). The optimum cut-off value for the flow index to predict pregnancy was 15.84 [area under the curve (AUC) 0.728, 95% CI 0.654-0.802; P = 0.001], and the combination of flow index and cancer antigen 125 (CA125) yielded improved predictive performance (AUC 0.805, 95% CI 0.740-0.870; P = 0.001). CONCLUSIONS: Endometrial blood perfusion is reduced in patients with internal ADM, and is associated with a lower pregnancy rate. The combination of flow index and serum CA125 provides an effective predictive model for clinical pregnancy prior to FET in this population.