The success of vaginal birth by use of trans-labial ultrasound plus vaginal examination and vaginal examination only in pregnant women with labor induction: a comparative study

Background: Predicting the success of vaginal delivery is an important issue in preventing adverse maternal and neonatal outcomes. Thus, this study aimed to compare the success rate of vaginal birth by using trans-labial ultrasound and vaginal examination, and vaginal examination only in pregnant women with labor induction.Methods: This was a comparative study including 392 eligible pregnant women with labor induction attending to a teaching hospital affiliated with Iran University of Medical Sciences from April to October 2018 in Tehran, Iran. Women were randomly assigned to two groups; the trans-labial ultrasound plus vaginal examination (group A), and the vaginal examination only (group B). Women were included in the study if they satisfied the following criteria: singleton pregnancy, 37 to 42 weeks of gestational age, fetal head presentation, a living fetus with no abnormalities, uncomplicated pregnancy, and no previous cesarean section or any uterine surgery. We used a partograph for both groups to assess the fetal head position and the fetal head station. In group 1, the Angle of Progression (AoP) and Rotation Angle (RA) were also assessed. Finally, the success and progression of vaginal delivery in two groups were compared by predicting the duration of delivery and mode of delivery.Results: The findings showed that 8.68% of women in the trans-labial plus vaginal examination group delivered by cesarean section, while 6.13% in the vaginal examination only group delivered by cesarean section (P = 0.55). In women with cesarean section in positive fetal head stations, Angle of Progression (AoP) was significantly decreased ranging from 90 to 135 degrees compared to women who delivered vaginally (135-180 degrees; P < 0.001). In addition, the Rotation Angle (RA) was significantly decreased in women with cesarean section ranging from 0 to 30 degrees compared to women who delivered vaginally (60-90 degrees; P < 0.001). Further analysis indicated that a higher risk of cesarean section was associated with vaginal examination only as compared to trans-labial ultrasound plus vaginal examination (HR: 8.65, P < 0.001).Conclusion: Angle of Progression (AoP) and Rotation Angle (RA) indexes might be useful parameters to predict labor progression and successful vaginal delivery among women undergoing labor induction.