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

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Abstract
Objective To evaluate the predictive value of angle of progression (AoP) for failed vacuum deliveries. Methods This prospective observational study included women with singleton pregnancies at a gestational age ≥ 37 weeks in cephalic presentation necessitating a vacuum extraction. Transperineal ultrasound was performed immediately before vacuum extraction, although AoP was measured only later, after delivery. Vacuum extraction was defined as failed when extraction duration exceeded 20 minutes or the cup detached more than 3 times. We compared demographic and ultrasonographic data for vacuum deliveries that failed and those that succeeded. The predictive value of AoP for failure of vacuum deliveries was calculated. Results AoP was measured in 235 women. Vacuum extractions failed for 30 (12.8%) women (29/184 nulliparas and 1/51 multipara) and resulted in 28 vaginal deliveries by forceps and 2 cesareans. The median [Q1‐Q3] AoP was significantly lower in the vacuum failure group: 136.6° [129.8‐144.1] versus 145.9° [135.0‐158.4] in the success group (P < .01). As all but one of the failed vacuum extractions occurred among nulliparas, the predictive value of AoP was calculated in this subgroup. The area under the ROC curve for prediction of vacuum extraction failure was 0.67 (95% CI, 0.57‐0.77) and the optimal AoP cutoff point 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 to choose between forceps and vacuum extraction.

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