The receiver-operator characteristic (ROC) curve for the different values of the resistance index concerning the discrimination between groups II and III. The values 0.7, 0.8, 0.9 and 1.0 are identified in the curve with a circle. The point in the curve that is closer to the upper-left corner of the plot corresponds to a value of 1 for the resistance index. At that cut-off point, the sensitivity and specificity values of the resistance index in the uterine artery were of 75% (CI 95%: 57.9%-86.8%) and 65.6% (48.3%-79.6%), respectively; the area under the curve (AUC) was 0.738 (0.676-0.799). The correspondent positive and negative predictive values were 89.9% and 32.8%, respectively. The likelihood ratio (LR) for a positive or negative test was 2.18 (CI 95%: 1.34%-3.55%) or 0.38 (CI 95%: 0.26%-0.56%), respectively.