A 32-year-old G2P1 at 40+2 weeks is in the second stage of labor. After 90 minutes of active pushing, the fetal head is at +1 station in right occipitoanterior (ROA) position. The obstetrician attempts vacuum extraction, but after three pulls with contractions, there is no descent of the fetal head. Which investigation should be performed next to determine the cause of failure and guide further management?

Explanation

## Investigation for Failed Vacuum Extraction **Key Point:** When vacuum extraction fails (no descent after 2–3 pulls), the next step is reassessment by vaginal examination under anesthesia to determine whether the failure is due to maternal factors (CPD, inadequate pelvis) or fetal factors (malposition, large baby). ### Rationale for Vaginal Examination Under Anesthesia **High-Yield:** Vaginal examination under anesthesia (VEU) is the investigation of choice because it: 1. Allows accurate reassessment of fetal station and position without maternal discomfort 2. Permits thorough pelvic assessment (diagonal conjugate, ischial spines, pelvic outlet) to exclude CPD 3. Guides the decision: proceed to cesarean delivery vs. attempt alternative instrumental delivery 4. Is rapid, non-invasive, and immediately actionable **Clinical Pearl:** Failed vacuum extraction is defined as: - No descent after 2–3 pulls with contractions, OR - Descent < 2 cm after 3 pulls, OR - Caput succedaneum or cephalohematoma after 3 pulls VEU helps differentiate: - **Cephalopelvic disproportion** (inadequate pelvis) → cesarean delivery - **Malposition** (OP, transverse) → reposition and retry, or cesarean - **High station** (>+2) → abandon vacuum, proceed to cesarean ### Why Other Investigations Are Inadequate | Investigation | Why Not Appropriate | | --- | --- | | **Pelvic X-ray** | Exposes mother and fetus to radiation; pelvimetry is unreliable; clinical assessment (VEU) is superior | | **Transabdominal ultrasound** | Cannot accurately measure descent in second stage; does not assess pelvic adequacy; time-consuming | | **Fetal scalp pH** | Measures fetal acid-base status, not the mechanical cause of failure; does not guide next management step | **Mnemonic: VEU REASSESS** — **V**aginal exam, **E**valuate station/position, **U**nder anesthesia; **R**eassess pelvis, **E**xclude CPD, **A**ssess adequacy, **S**elect next step, **S**afe decision-making, **E**ither retry or cesarean, **S**S**S**. **Warning:** A common trap is choosing ultrasound or X-ray for pelvimetry. However, clinical assessment via VEU is the gold standard in labor. Imaging is not indicated in the acute setting of failed instrumental delivery.