Vacuum extraction is successful in 95% of cases with an occiput posterior position: the results of a prospective, multicenter study.

Background: Occiput posterior position is associated with labor arrest, need for operative delivery, and failed instrumental vaginal delivery, with resulting adverse peripartum outcomes. Vacuum extraction is the most commonly performed type of instrumental delivery worldwide. Objective: This study aimed to investigate the outcome of vacuum extraction in fetuses with sonographically confirmed occiput posterior position before the procedure. Study design: Singleton pregnancies at term with sonographically confirmed fetal occiput posterior position before the vacuum extraction were enrolled in 3 academic maternity units. Fetal head station was assessed using transperineal sonography measuring the angle of progression and the head-perineum distance. The primary outcome was failed vacuum extraction, defined as the need for cesarean delivery. Secondary outcomes included adverse maternal and/or adverse neonatal outcomes and complicated vacuum extraction, with the latter defined as failed vacuum extraction or at least 3 out of the following 6 parameters: 5-minute Apgar score <7, neonatal acidemia, admission to the neonatal intensive care unit, neonatal trauma, postpartum hemorrhage, and obstetrical anal sphincter injuries. Results: Among the 98 patients included in the study, vacuum extraction was successful in 94 (96%). Logistic regression analysis showed that the measurement of the head-perineum distance was the only factor independently associated with failed vacuum extraction (odds ratio, 1.25; 95% confidence interval, 1.02-1.55; P=.03), with an area under the curve of 0.79 (P=.04). A head-perineum distance cutoff value of 38.5 mm discriminated between successful and failed vacuum extraction, yielding a sensitivity of 75.0% (3/4), specificity of 84.0% (79/94), positive likelihood ratio of 4.7, and negative likelihood ratio of 0.3. Conclusion: Vacuum extraction is successful in 95% of fetuses with occiput posterior position confirmed at ultrasound. The head-perineum distance measured at transperineal ultrasound has a significant albeit weak association with the outcome of vacuum extraction.