Intrapartum Ultrasound in Vacuum Operative Delivery: A Comprehensive Review and Proposal of the Novel Ultrasound Flexion Point Method

Operative vaginal delivery (OVD) via vacuum extraction is a fundamental component of modern obstetric management, yet it carries specific risks of failure and maternal-fetal complications, such as cup detachment, cephalohematoma, and intracranial hemorrhage. The success and safety of the procedure rely heavily on the correct application of the vacuum cup over the "flexion point" of the fetal head. Traditional identification of this landmark via digital examination is often hindered by caput succedaneum and cranial molding, leading to high rates of diagnostic error, particularly in dystocic labor, due to fetal head malpositions and malpresentation. Intrapartum ultrasound (ITU) has demonstrated superior accuracy compared to clinical examination in assessing fetal head position and station and internal rotation. This expert commentary and technical proposal analyzes the current literature regarding vacuum extraction application and failures, focusing on the predictive value of ITU parameters (e.g., Angle of Progression, Midline Angle, Head-Symphysis Distance) and the impact of ITU on cup placement and delivery outcomes. Furthermore, we propose a novel technique: the "Ultrasound Flexion Point" (UFP). This method utilizes translabial ultrasound to identify the specific intersection of the fetal midline and the biparietal diameter as an objective sonographic proxy for the classical flexion point. By providing spatial orientation guidance immediately before the procedure, this technique aims to guide the operator in aligning the cup's notch with the sonographically identified target zone, using the midline angle as orientation reference, thereby potentially minimizing paramedian or deflexing applications and reducing the incidence of vacuum detachment and associated neonatal trauma. This expert commentary and technical proposal synthesizes current evidence and proposes a protocol requiring prospective validation through randomized controlled trials.