Angle of fetal head progression measured using transperineal ultrasound as a predictive factor of vacuum extraction failure.

OBJECTIVE: To evaluate the predictive value of angle of progression (AoP) of the fetal head for a failed vacuum delivery. METHODS: This was a prospective observational study that included women with a singleton pregnancy of ≥ 37 weeks' gestation, in cephalic presentation requiring vacuum extraction. Transperineal ultrasound was performed immediately before vacuum extraction, although AoP was measured on stored images after delivery. Vacuum extraction was defined as failed when the duration of extraction exceeded 20 min or the vacuum cup detached more than three times. We compared the demographic and ultrasound data of failed vacuum deliveries with those that were successful. The predictive value of AoP for failure of vacuum delivery was calculated. RESULTS: AoP was measured in 235 women. Vacuum extractions failed in 30 (12.8%) women (29/184 nulliparous and 1/51 parous) and resulted in 28 vaginal deliveries by forceps and two Cesarean deliveries. Median AoP was significantly lower in the vacuum failure group compared with those with successful vacuum delivery (136.6° (interquartile range (IQR), 129.8-144.1°) vs 145.9° (IQR, 135.0-158.4°); P < 0.01). As all but one failed vacuum extraction occurred among nulliparous women, the predictive value of AoP was calculated in this subgroup of women. The area under the receiver-operating characteristics curve for prediction of vacuum extraction failure was 0.67 (95% CI, 0.57-0.77) and the optimal AoP cut-off was 145.5°. Above this value, the rate of vacuum extraction failure fell below 5%. CONCLUSION: AoP is a predictive factor of failed vacuum extraction, especially among nulliparous women whose risk of failure is high. AoP measurement may help in choosing between forceps and vacuum extraction. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.