ROC analyses on the cleavage-stage ET cohort
ROC analysis was performed on the cleavage-stage ET cohort, and the ROC curve for the average distance between the midline of the uterine cavity and the ultrasound probe indicated that the cut-off value of 2.146 cm showed 77.2% sensitivity and 52.2% specificity in predicting clinical pregnancy, with an area under the ROC curve of 0.667 (P = 0.001). Additionally, the cut-off value of 2.146 cm showed 72.1% sensitivity and 51.7% specificity in predicting live birth, with an area under the ROC curve of 0.632 (P = 0.011) (Figure S3).