Predicting the Probability of Clinical Pregnancy Following Fresh Embryo Transfer in Women Undergoing In Vitro Fertilization: A Nomogram Based on Multimodal Ultrasonographic Parameters and Serum Anti-Müllerian Hormone

Background: We developed and externally validated a model for estimating the probability of clinical pregnancy after in vitro fertilization and fresh embryo transfer using routinely available laboratory and multimodal ultrasonographic measures. Methods: This two-center retrospective study included 451 women in the development cohort and 229 women in the external validation cohort. Eleven candidate predictors were evaluated using Group LASSO-penalized logistic regression with stratified 10-fold cross-validation. Continuous predictors were assessed for nonlinearity using restricted cubic splines, and the complete model-development procedure was repeated in 1000 bootstrap resamples. Model performance was assessed by discrimination, calibration, overall prediction error, and decision curve analysis. Results: The final model included female age, serum anti-müllerian hormone (AMH), endometrial thickness, endometrial volume, and vascularization flow index (VFI). The apparent area under the receiver operating characteristic curve (AUC) was 0.864 (95% confidence interval [CI], 0.826–0.898) in the development cohort; the optimism-corrected AUC was 0.842. The optimism-corrected calibration intercept, calibration slope, Brier score, and maximum absolute calibration error (Emax) were 0.002, 1.051, 0.163, and 0.045, respectively. In external validation, the AUC was 0.810 (95% CI, 0.750–0.868), the calibration intercept was −0.106, the calibration slope was 0.900, the Brier score was 0.177, and Emax was 0.070. Decision curve analysis indicated net benefit over selected threshold probabilities. Conclusions: The model showed good discrimination and generally satisfactory calibration. It may support individualized counseling before fresh embryo transfer, but prospective validation in larger and more diverse populations is required.