The Clinical Pregnancy Rate of Ethinylestradiol/Cyproterone Acetate Downregulation Protocol Is Not Inferior to That of the Conventional Gonadotropin-Releasing Hormone-Analogs Downregulation Group: A Randomized Controlled Trial

Background: Downregulation of the hypothalamic/pituitary axis is a critical step in patients undergoing controlled ovarian hyperstimulation (COH). The aim of this study was to compare clinical pregnancy rates between gonadotropin-releasing hormone-analogs (GnRH-a) and ethinylestradiol/cyproterone acetate (EE/CPA) downregulation protocols in assisted reproductive technology (ART). Methods: A total of 392 patients received EE/CPA, while 392 patients were treated with Triptorelin Acetate (0.1 mg) or Diphereline as the control group. 1–2 embryos were transferred, and the primary outcome measure was the clinical pregnancy rate. Secondary outcomes included the number of oocytes, mature oocytes, fertilized oocytes, good-quality embryos, mature oocyte rate, fertilization rate, cleavage rate, viable embryo rate, good-quality embryo rate, implantation rate, and the incidence of ovarian hyperstimulation syndrome (OHSS). In addition, the economic cost was compared between groups. Results: There were no significant differences in the clinical pregnancy rates between the EE/CPA and control groups (50.4% vs. 51.9%, p = 0.630). In the EE/CPA group, the numbers of oocytes retrieved (14.67 vs. 14.78, p = 0.809), mature oocytes (12.95 vs. 13.24, p = 0.459), fertilized oocytes (11.59 vs. 12.11, p = 0.154), viable embryo rate (47.5% vs. 49.2%, p = 0.099), good-quality embryos (4.98 vs. 5.19, p = 0.311), good-quality embryos rate (43.0% vs. 42.8%, p = 0.846), as well as the implantation rate (37.0% vs. 38.0%, p = 0.741), were comparable to those of the control group. The mature oocyte rate (88.3% vs. 89.6%, p = 0.023), fertilization rate (89.5% vs. 91.5%, p < 0.001), number of viable embryos (5.51 vs. 5.96, p = 0.026) were lower than that in the control group, while the cleavage rate (98.0% vs. 96.8%, p < 0.001) was higher. The incidence of OHSS was significantly lower in EE/CPA group (0.0% vs. 2.0%, p = 0.008). The economic cost of the EE/CPA group was significantly lower than that in the control group. Conclusions: Compared with the GnRH-a downregulation protocol, the EE/CPA protocol yielded comparable outcomes. Thus, EE/CPA may represent a viable alternative for COH, offering greater flexibility and lower cost. Clinical Trial Registration: The study has been registered on: https://www.chictr.org.cn/ (registration number: ChiCTR2100048310; registration link: https://www.chictr.org.cn/showproj.html?proj=125733).