Identifying cycle-specific predictive factors for clinical pregnancy after recurrent implantation failure: a retrospective cohort study

To investigate whether the clinical predictors of achieving a clinical pregnancy differ between fresh and frozen embryo transfer cycles in patients with recurrent implantation failure (RIF) undergoing their first ART treatment after diagnosis. This retrospective study reviewed 24,070 ART cycles performed at Peking University Third Hospital from 2021 to 2023 among patients with at least two documented embryo transfer cycles. Patients diagnosed with RIF were identified, and the first transfer cycle following diagnosis was assessed. After applying strict inclusion and exclusion criteria, 377 fresh and 922 frozen cycles were included. Clinical, hormonal, endometrial, and procedural characteristics were collected. Clinical pregnancy was defined as the primary outcome. Predictive factors were evaluated using univariate and multivariate logistic regression models. Independent predictors of clinical pregnancy included younger age (OR = 0.939, 95% CI: 0.912–0.967, p < 0.001), higher AMH levels (OR = 1.045, 95% CI: 1.002–1.089, p = 0.039), elevated androgen (OR = 1.031, 95% CI: 1.004–1.059, p = 0.026), lower FSH (OR = 0.955, 95% CI: 0.913–0.998, p = 0.040), and greater endometrial thickness (OR = 1.057, 95% CI: 1.013–1.103, p = 0.011). The predictive factors differed between cycle types. In fresh cycles, the number of transferable embryos and the use of long or ultra-long stimulation protocols were additional significant predictors. In frozen cycles, only age, AMH, and endometrial thickness remained significant. Predictors of clinical pregnancy in RIF patients differ between fresh and frozen embryo transfer cycles. Younger maternal age, favorable ovarian reserve (reflected by higher AMH and lower FSH), elevated androgen, and greater endometrial thickness are overall associated with higher pregnancy likelihood. Embryo availability and stimulation protocol further influence outcomes in fresh cycles, whereas frozen cycles exhibit a more limited predictor profile focused on patient ovarian reserve and endometrial conditions.