Intrapartum sonographic assessment of the fetal head flexion in protracted active phase of labor and association with labor outcome: a multicenter, prospective study

Background: To date, no research has focused on the sonographic quantification of the degree of flexion of the fetal head in relation to the labor outcome in women with protracted active phase of labor. Objective: This study aimed to assess the relationship between the transabdominal sonographic indices of fetal head flexion and the mode of delivery in women with protracted active phase of labor. Study Design: Prospective evaluation of women with protracted active phase of labor recruited across 3 tertiary maternity units. Eligible cases were submitted to transabdominal ultrasound for the evaluation of the fetal head position and flexion, which was measured by means of the occiput-spine angle in fetuses in nonocciput posterior position and by means of the chin-to-chest angle in fetuses in occiput posterior position. The occiput-spine angle and the chin-to-chest angle were compared between women who had vaginal delivery and those who had cesarean delivery. Cases where obstetrical intervention was performed solely based on suspected fetal distress were excluded. Results: A total of 129 women were included, of whom 43 (33.3%) had occiput posterior position. Spontaneous vaginal delivery, instrumental delivery, and cesarean delivery were recorded in 66 (51.2%), 17 (13.1%), and 46 (35.7%) cases, respectively. A wider occiput-spine angle was measured in women who had vaginal delivery compared with those submitted to cesarean delivery owing to labor dystocia (126±14 vs 115±24; P<.01). At the receiver operating characteristic curve, the area under the curve was 0.675 (95% confidence interval, 0.538–0.812; P<.01), and the optimal occiput-spine angle cutoff value discriminating between cases of vaginal delivery and those delivered by cesarean delivery was 109°. A narrower chin-to-chest angle was measured in cases who had vaginal delivery compared with those undergoing cesarean delivery (27±33 vs 56±28 degrees; P<.01). The area under the curve of the chin-to-chest angle in relation to the mode of delivery was 0.758 (95% confidence interval, 0.612–0.904; P<.01), and the optimal cutoff value discriminating between vaginal delivery and cesarean delivery was 33.0°. Conclusion: In women with protracted active phase of labor, the sonographic demonstration of fetal head deflexion in occiput posterior and in nonocciput posterior fetuses is associated with an increased incidence of cesarean delivery owing to labor dystocia. Such findings suggest that intrapartum ultrasound may contribute in the categorization of the etiology of labor dystocia.