Fetal head-symphysis distance and mode of delivery in the second stage of labor

Abstract

Objective. To evaluate whether the fetal head-symphysis distance measured by three-dimensional transperineal ultrasound during the active second stage predicts operative delivery. Design. Prospective observational study. Setting. University hospital, Bologna, Italy. Population. Seventy-one nulliparous women at term in active second stage of labor. Methods. We acquired a series of sonographic volumes at the beginning of the active second stage (T1) and every 20 min thereafter (T2, T3, T4, T5, T6) until delivery. All volumes were retrospectively analyzed and head-symphysis distance was measured for each acquisition. We compared head-symphysis distance between women with spontaneous vaginal delivery and those with operative delivery. Receiver operator characteristic curves were constructed to estimate the accuracy of head-symphysis distance in the prediction of operative delivery. Logistic regression was used to identify independent variables associated with operative delivery. Main outcome measures. Operative delivery (vacuum or cesarean). Results. Of the women included, 81.7% had a spontaneous vaginal delivery and 18.3% underwent operative delivery. Women with spontaneous vaginal delivery had shorter head-symphysis distance than women in the operative delivery group at T1 (p < 0.001), T2 (p < 0.001) and T3 (p = 0.025), whereas no significant differences were recorded thereafter. Receiver operator characteristic curves revealed accuracy values of 81.0%, 87.9% and 77.6% in the prediction of operative delivery at T1, T2 and T3, respectively. At multivariate logistic regression head-symphysis distance and epidural analgesia were the only independent predictors of operative delivery among ultrasonographic, maternal and intrapartum variables. Conclusions. Ultrasonographic measurement of head-symphysis distance in the second stage of labor can be used to predict operative delivery.