P-434 Association of estrogen receptor alpha expression with endometrial receptivity and pregnancy outcomes

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Abstract Study question Does estrogen receptor alpha (ERα) expression vary across different endometrial receptivity stages, and is it associated with age and pregnancy outcomes? Summary answer ERα expression significantly differs among Endometrial Receptivity Array (ERA)-defined stages and correlates with pregnancy outcomes but not with age. What is known already Estrogen receptor alpha (ERα) plays a pivotal role in regulating endometrial receptivity by mediating estrogen-driven proliferation, differentiation, and immune modulation. Optimal ERα expression during the implantation window supports a receptive endometrial environment, whereas dysregulation is linked to impaired implantation and reduced pregnancy success. The Endometrial Receptivity Array (ERA) is widely used to assess endometrial status and optimize embryo transfer timing. However, the precise role of ERα across different ERA-defined receptivity stages and its association with clinical outcomes remains insufficiently understood. Study design, size, duration This retrospective study analyzed 150 endometrial biopsy samples from patients undergoing in vitro fertilization (IVF) between January 2020 and December 2022. Samples were categorized based on ERA results, age, and pregnancy outcomes, and ERα expression was evaluated. Participants/materials, setting, methods The study was conducted at Lee Women’s Hospital, Taiwan. Among the 150 endometrial biopsy samples collected, 126 were analyzed after excluding those lacking ERA data, unavailable immunohistochemistry (IHC) slides, or cases without embryo transfer. ERα expression was evaluated using IHC staining and quantified with ImageJ software. Statistical analyses, including one-way ANOVA and t-tests, were conducted to compare ERα expression across different ERA stages, age groups, and pregnancy outcomes, with p < 0.05 considered statistically significant. Main results and the role of chance ERα expression varied significantly across ERA stages (p < 0.001), with the highest levels observed in the receptive stage (ER score: 1.38). Although ERα expression showed a decreasing trend with age, no significant differences were detected between age groups (p = 0.5625). Notably, ERα expression was significantly lower in the pregnant group (ER score: 1.26) than in the non-pregnant group (ER score: 1.38, p < 0.001). Furthermore, ERα expression during the early-receptive (p = 0.036) and receptive (p < 0.0001) stages was significantly associated with pregnancy outcomes, whereas expression in the late-receptive (p = 0.1285) and post-receptive (p = 0.142) stages showed no significant correlation with pregnancy success. These findings suggest that ERα is a key regulator of endometrial receptivity and implantation success, particularly within the receptive window, and may hold predictive value for implantation potential. Limitations, reasons for caution This retrospective study had limited sample sizes in some ERA stages, potentially affecting generalizability. Larger prospective studies are needed to confirm these findings and further explore ERα’s role in endometrial receptivity. Wider implications of the findings ERα may serve as a potential biomarker for endometrial receptivity, facilitating the optimization of embryo transfer timing. Moreover, therapeutic modulation of ERα expression during implantation may offer a novel approach to improving fertility outcomes in patients experiencing implantation failure. Trial registration number Yes

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