Prospective evaluation of the uterocervical angle as a predictor of spontaneous preterm birth.

INTRODUCTION: The uterocervical angle has been proposed as an ultrasound marker to predict spontaneous preterm birth; however, the studies that provided this evidence were retrospective and their results heterogeneous. This study aimed to assess the ability of the uterocervical angle to predict spontaneous preterm birth before 34 and 37 weeks of gestation. MATERIAL AND METHODS: A prospective cohort study with singleton pregnancies between 19.0 and 22.6 weeks of gestation. Uterocervical angle and cervical length were measured by transvaginal ultrasound. Maternal history and pregnancy data were recorded. Delivery data were subsequently collected. RESULTS: The final analysis included 1453 singleton pregnancies. Spontaneous preterm birth before 37 weeks occurred in 52 cases (3.6%) and before 34 weeks in 17 (1.2%). For the prediction of spontaneous preterm birth before 34 weeks, the area under the curve for the uterocervical angle was 0.67 (95% CI, 0.54 - 0.79) and the detection rate 5.9% and 23.5% for a fixed false-positive rate of 5% and 10%, respectively. For the prediction of spontaneous preterm birth before 37 weeks, the area under the curve was 0.58 (95% CI, 0.50 - 0.67) and the detection rate 5.8% and 18% for a fixed false-positive rate of 5% and 10%, respectively. Combined predictive models were studied. To predict spontaneous preterm birth before 34 weeks, the best model was provided by a combination of uterocervical angle and cervical length (area under the curve 0.72; 95% CI, 0.58 - 0.86). The detection rate of this model was 35.3% and 41.2% for a fixed false-positive rate of 5% and 10%, respectively. To predict spontaneous preterm birth before 37 weeks, the best model was provided by a combination of uterocervical angle, cervical length and previous history of spontaneous preterm birth (area under the curve 0.64; 95% CI, 0.55 - 0.72). The detection rate of this model was 15.4% and 30.8% for a fixed false-positive rate of 5% and 10%, respectively. Obese women and those with a history of cesarean section had a wider uterocervical angle. CONCLUSIONS: The uterocervical angle, measured mid-trimester, is a poor predictor of spontaneous preterm birth.