The ability of ultrasound to predict postpartum hemorrhage remains poorly described. The aim of this study was to evaluate whether ultrasound measurement of intrauterine content can predict blood loss and postpartum hemorrhage after vaginal delivery. We used a preliminary prospective monocentric study of 201 women who delivered vaginally after 34 wk of gestation. Measurements were performed 30-45 min after normal vaginal delivery according to strict ultrasonographic criteria. Analysis of the relationship between ultrasound measurements and hemoglobin loss showed a strong linear correlation (R² = 0.59 and R² = 0.4 for isthmic and fundal measurements). The maximal value between the fundal and isthmic measurements seems to provide the best accuracy to predict loss of hemoglobin higher than 3 g/dL (area under the curve [AUC] of the receiver operating characteristic curve, 0.9; 95% confidence interval [CI], [0.76-0.97]) and post-partum hemorrhage (AUC, 0.99; 95%CI, [0.984-0.99]). In case of intrauterine content >2 cm (135/201), the risks of loss of hemoglobin higher than 3 g/dL (5/135 vs. 0/66) and post-partum hemorrhage (11/135 vs. 0/66) were increased, all the more if the intrauterine content was >4 cm (4/16 and 11/16, respectively). Considering the maximal measurement, the most optimal cut-off value for clinical practice could be 2.4 cm (sensibility 100%, specificity 57%) and 4.1 cm (sensibility 100%, specificity 97%) for loss of hemoglobin higher than 3 g/dL and post-partum hemorrhage, respectively.