Vacuum extraction effective in fetuses with ultrasound-confirmed occiput posterior position, suggests study

A new study published in the American Journal of Obstetrics and Gynecology showed that 95% of fetuses with an occiput posterior (OP) position verified by ultrasonography successfully undergo vacuum extraction (VE). About 5% of women in the second stage of labor are in the persistent occiput-posterior position, which increases the risk of labor complications such as a 50% chance of labor arrest during the second stage, a 60% chance of cesarean or instrumental vaginal delivery, and a nearly 20% chance of obstetric anal sphincter injuries.

The gold standard for determining the position of the fetus during labor is a digital vaginal examination. However, it has been demonstrated that clinical examinations are not always accurate in diagnosing occiput position, particularly when non-occiput anterior position is present and before an instrumental delivery is performed.

Negative peripartum outcomes are linked to occiput-posterior position, labor arrest, the requirement for a surgical birth, and unsuccessful instrumental vaginal delivery. The most widely used method of instrumental delivery in the world is vacuum extraction. This study was set to examine the effects of VE in fetuses whose OP position was validated sonographically before the surgery.

3 academic maternity units enrolled singleton pregnancies at term with fetal OP position established by sonography before the vacuum extraction. Transperineal sonography was used to measure the head-perineum distance (HPD) and the angle of progression (AoP) at the fetal head station. The need for a cesarean birth, or failed VE, was the main result.

Negative outcomes for the mother and/or the newborn were secondary outcomes, as was complicated VE, which was defined as failed VE or at least three of the following 6 parameters as neonatal trauma, postpartum hemorrhage, obstetric anal sphincter injuries, neonatal acidemia, admission to the neonatal intensive care unit, and Apgar <7 at 5 minutes.

VE was effective in 94 (96%), out of the 98 patients that were part of the trial. With an area-under-the-curve of 0.79, logistic regression analysis demonstrated that the head-perineum distance (HPD) measurement alone was independently linked with failed VE. Successful and unsuccessful VE were distinguished by an HPD cut-off value of 38.5 mm, which produced a specificity of 84.0% (79/94), sensitivity of 75.0% (3/4), LHR+ of 4.7, and LHR- of 0.3. Overall, this study showed that fetuses with sonographically detected persistent OP position in the second stage of labor had a high VE success rate and a low risk of maternal and fetal complications.

Reference:

Falcone, V., Dall’Asta, A., Romano, A., Mappa, I., Geron, Y., Bontempo, P., Salluce, M., Di Pasquo, E., Morganelli, G., Di Serio, M., Fieni, S., Gilboa, Y., Rizzo, G., & Ghi, T. (2024). Vacuum extraction is successful in 95% of cases with an occiput posterior position: the results of a prospective, multi-center study. In American Journal of Obstetrics and Gynecology. Elsevier BV. https://doi.org/10.1016/j.ajog.2024.12.022