What is the best transperineal ultrasound parameter for predicting success of vacuum extraction?

We read with great interest the Editorial/Opinion by Yeo and Romero1 and three papers2-4 on the application of intrapartum transperineal ultrasound at the second stage of labor in the March issue of Ultrasound in Obstetrics and Gynecology. Henrich et al.5 first reported three parameters on translabial ultrasound at the second stage of labor to predict the success of vacuum extraction. These could be grouped into descent (subjective assessment during maternal pushing and passage of the fetal head below the infrapubic line) and direction of the fetal head. Similarly, Ghi et al.4 focused on direction and rotation of the fetal head. Barbera et al.2 and Kalache et al.3 used the ‘angle of descent/progression’ as an alternative parameter to assess the descent of the fetal head. We would like to report our preliminary transperineal ultrasound findings on 20 patients with prolonged second stage of labor, collected from October 2006 to March 2009 (Table 1). Ultrasound is commonly used in our labor ward. Patients verbally consented to the examination. Using the ultrasound parameters as described by Henrich et al.5, 15 patients with favorable parameters were successfully delivered by simple vacuum extraction. Second-stage Cesarean sections were performed on clinical grounds for the other five patients, taking into account the unfavorable ultrasound findings. Four of these fetuses were in an occipitoposterior position and three showed no descent. All five fetal heads were in a horizontal or downward direction. We measured the angle of progression for all these patients retrospectively. Interestingly, the angle of progression at rest2, 3 did not differ between the group delivered by vacuum extraction and the group having Cesarean section. On the other hand, the angle of progression during maternal pushing differed between the two groups. We also calculated the change in angle of progression from when the mother was at rest to when she was pushing. Using a cut-off of 150° for the angle of progression during maternal pushing, we could predict 12 of the 15 (80%) successful vacuum extractions and all five Cesarean sections. Similarly, a change in angle of more than 15° could predict 11 of the 15 (73%) successful vacuum extractions and all five Cesarean sections. Note that the sample size was small in all of the studies discussed. A large prospective study is required to determine the best transperineal ultrasound predictor(s) for successful vacuum extraction in the second stage of labor. W.-L. Lau*, W.-C. Leung*, R.