To identify the optimal dominant follicle size for human chorionic gonadotropin (hCG) trigger in intrauterine insemination (IUI) cycles and to establish predictive models for clinical outcomes. A retrospective cohort study of 2,275 IUI cycles conducted between 2017 and 2023 was performed. Cycles were stratified into 10 groups according to dominant follicle diameter on the trigger day. Clinical pregnancy, positive β-hCG rate, and live birth rates were compared. Multivariate logistic regression was applied to identify independent predictors, and nomogram models were developed to predict outcomes. Model performance was assessed using receiver operating characteristic (ROC) curves, calibration plots, and decision curve analysis (DCA). Overall, 287 clinical pregnancies were achieved (12.62%). The highest clinical pregnancy rates were observed in the 17.0–17.5 mm (15.25%) and 18.0–18.5 mm (15.71%) follicle size groups, both of which were significantly higher than those in the other groups. Independent predictors of pregnancy outcomes included infertility duration, body mass index (BMI), and anti-Müllerian hormone (AMH) level. The nomogram models demonstrated moderate discriminative ability, with an area under the curve (AUC) of 0.72 for clinical pregnancy and 0.70 for positive β-hCG. The models showed good calibration and favorable clinical utility in decision curve analysis (DCA). The optimal follicle size for hCG trigger in IUI cycles is 17.0–18.5 mm. Ovarian reserve and BMI remain crucial determinants of success, highlighting the importance of individualized timing strategies.
zhao et al. (Sat,) studied this question.