Transperineal sonographic assessment of angle of progression as a predictor of successful vaginal delivery following induction of labor.

OBJECTIVES: To assess whether measurement of the angle of progression (AOP) before induction of labor (IOL) can predict successful vaginal delivery in nulliparous women. METHODS: This was a prospective, observational study of nulliparous women with a singleton term pregnancy and an indication for IOL. Transperineal sonography was used to measure the AOP before cervical ripening. Since all women enrolled had a low Bishop score, 98.6% of them were induced with either intracervical extra-amniotic balloon catheter or vaginal prostaglandin E-2. The staff in the labor ward were blinded to the AOP measurements. Clinical data were retrieved from computerized medical records. RESULTS: Of the 150 women included in the final analysis, 40 (26.7%) delivered by Cesarean section. The median AOP was narrower in women who had a Cesarean delivery than in those who delivered vaginally (90° (interquartile range (IQR), 84-94.5°) vs 98° (IQR, 90.8-105°); P < 0.001). When including only women who underwent Cesarean delivery for non-progression of labor (n = 27) in the analysis, an AOP of > 92° (derived from a receiver-operating characteristics curve) was associated with a successful vaginal delivery in 94.8% of women. Multivariate stepwise logistic regression analysis including maternal age, body mass index, gestational age, estimated fetal weight, fetal head station, indication for IOL and AOP demonstrated that only AOP was independently associated with the prediction of a successful induction. CONCLUSION: AOP may be a useful sonographic parameter for predicting successful vaginal delivery among nulliparous women at term undergoing IOL; an AOP wider than 92° is associated with a high rate of vaginal delivery. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Can angle of progression in pregnant women before onset of labor predict mode of delivery?

OBJECTIVES: The angle of progression (AOP), measured by transperineal ultrasound, has been used to assess fetal head descent during labor. Our aim was to assess whether, before onset of labor, parous women have a narrower AOP than do nulliparous women and if a narrow AOP is associated with a higher rate of Cesarean delivery. METHODS: In this prospective, observational study, we performed transperineal ultrasound in pregnant women not yet in labor at ≥ 39 weeks' gestation who delivered within 1 week of sonography. The AOP was compared as follows: in nulliparous women, between those who had a Cesarean section and those who delivered vaginally; and among women who delivered vaginally, between those who were nulliparous and those who were parous. RESULTS: Included in the study were 100 nulliparous and 71 parous women. Among those who delivered vaginally (n = 161), the median AOP before onset of labor was narrower in parous than in nulliparous women (98° (interquartile range (IQR)), 90-107° vs 104° (IQR, 97-113°), P < 0.001). Among the 100 nulliparous women, (1) the median AOP before onset of labor was narrower in those who went on to deliver by Cesarean section (n = 9) than in those delivered vaginally (n = 91) (90° (IQR, 85.5-93.5°) vs 104° (IQR, 97-113°), P < 0.001); (2) an AOP ≥ 95° (derived from the receiver-operating characteristics curve) was associated with vaginal delivery in 99% of women; and (3) 89% (8/9) of women who delivered by Cesarean section had an AOP < 95°. Among the 71 parous women, only one delivered by Cesarean section and all of those with an AOP < 95° delivered vaginally. CONCLUSION: A narrow AOP (< 95°) in non-laboring nulliparous women at term is associated with a high rate of Cesarean delivery. Parous women have a narrower AOP than do nulliparous women before the onset of labor; however, unlike in nulliparous women, a narrow AOP in parous women does not appear to be associated with Cesarean delivery and most parous women with such an angle go on to deliver vaginally.