Intrapartum translabial ultrasound (ITU): sonographic landmarks and correlation with successful vacuum extraction.

Objective: Having studied intrapartum translabial ultrasound (ITU) to define easily obtainable sonographic criteria during maternal pushing, we used it dynamically immediately before vacuum extraction to determine its use in predicting successful operative vaginal delivery.

Methods: In a pilot study, maternal and fetal landmarks were determined sonographically during maternal pushing from a mid-sagittal translabial insonation using a curved array transducer in women delivering singleton fetuses in cephalic presentation spontaneously. With this transducer placed infrapubically ('infrapubic plane'), easily obtainable landmarks and signs were: (i) the 'infrapubic line', perpendicular to the long axis of the pubic joint and extending dorsally from its inferior margin in a mid-sagittal plane, (ii) the widest fetal head diameter and its movement with regard to the infrapubic line during pushing, and (iii) the 'head direction' with respect to the long axis of the symphysis. A three-dimensional reconstruction from a computed tomographic (CT) dataset of a normal female pelvis was then used to quantify accurately the spatial relationship between the infrapubic line and the anatomical landmarks. Finally, 20 pregnant women in spontaneous term labor with normal singleton fetuses in cephalic presentation and clinical indication for vacuum extraction were studied by ITU immediately before operative vaginal delivery.

Results: CT reconstruction demonstrated the infrapubic line to be 3 cm cranial to the parallel interspinous plane. Eleven of the 20 vacuum deliveries with the 'head-up' sign (head pointing ventrally) and objective descent of the fetal head below the infrapubic line, both noted at the height of pushing, resulted in successful ('simple' or 'moderately difficult') operative delivery. Lack of descent or lack of passage below the infrapubic line and horizontal or downward head direction were poor prognostic signs.

Conclusions: ITU provides objective information on the dynamics of the second stage of labor, head station and head direction. ITU may be used to assess the prognosis for operative vaginal delivery.