A 28-year-old primigravida at term is in active labor. After 2 hours of pushing in the second stage, the fetal head is at +2 station with occipitoposterior (OP) position. The obstetrician decides to apply vacuum for assisted delivery. Before proceeding, which investigation is most appropriate to confirm fetal well-being and exclude cephalopelvic disproportion?

Explanation

## Assessment Before Vacuum-Assisted Delivery **Key Point:** Before applying vacuum extraction, fetal well-being must be confirmed and maternal-fetal compatibility assessed. CTG with variability is the standard investigation of choice. ### Why CTG is the Investigation of Choice **High-Yield:** Cardiotocography (CTG) is the most appropriate investigation because it: 1. Confirms fetal well-being in real-time (normal baseline FHR 110–160 bpm, good variability) 2. Detects decelerations that would contraindicate vacuum use 3. Is non-invasive, rapid, and immediately available 4. Guides the decision to proceed with instrumental delivery **Clinical Pearl:** A reactive CTG with good variability (5–25 bpm) and absence of concerning decelerations is mandatory before vacuum application. Fetal tachycardia, reduced variability, or late decelerations are relative contraindications. ### Role of Other Investigations | Investigation | Role in Vacuum Delivery | Why Not First Choice | | --- | --- | --- | | **Transabdominal ultrasound** | Can assess pelvimetry if clinical pelvic adequacy is uncertain | Ultrasound pelvimetry is less accurate than clinical assessment; not standard pre-vacuum protocol | | **Fetal scalp blood sampling** | Reserved for abnormal CTG to differentiate fetal hypoxia from artifact | Invasive; not used as routine pre-vacuum assessment | | **MRI pelvis** | Useful in suspected CPD or when vaginal delivery is contraindicated | Time-consuming; not practical in active labor; reserved for antenatal counseling | **Mnemonic: VACUUM PRE-CHECK** — **V**ariability on CTG, **A**bsence of decelerations, **C**onfirm fetal well-being, **U**se only if reassuring. **Warning:** Do not proceed with vacuum if CTG is non-reassuring (absent variability, repetitive late decelerations, fetal bradycardia). This is a common trap — students may think ultrasound pelvimetry is needed, but clinical pelvimetry is adequate if CPD is not suspected clinically.