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