## Investigation of Choice for Assessing Fetal Well-Being Before Instrumental Delivery ### Clinical Context In a prolonged second stage with signs of fetal stress (caput, molding), the obstetrician must confirm that operative vaginal delivery is truly indicated and that the fetus can tolerate the procedure. ### Why Cardiotocography (CTG) is the Answer **Key Point:** CTG with continuous fetal heart rate pattern assessment is the standard investigation to evaluate fetal well-being immediately before instrumental delivery. It allows real-time assessment of: - Baseline fetal heart rate - Variability - Accelerations and decelerations - Response to uterine contractions **Clinical Pearl:** A reassuring CTG pattern (baseline 110–160 bpm, normal variability, accelerations present, no late decelerations) supports proceeding with instrumental delivery. A non-reassuring pattern may prompt escalation to cesarean delivery instead. **High-Yield:** CTG is non-invasive, rapid, and can be repeated serially. It is the **first-line investigation** before any operative vaginal delivery attempt. ### Comparison of Investigations | Investigation | Timing | Indication | Limitation | |---|---|---|---| | **CTG** | Immediate, continuous | Routine fetal well-being before instrumental delivery | Subjective interpretation | | Fetal scalp blood gas | During labor if CTG non-reassuring | Confirm metabolic acidosis when CTG is ambiguous | Invasive; requires cervical dilation; not first-line | | Fetal pulse oximetry | During labor (rarely used) | Adjunct if CTG non-reassuring | Not widely available; limited evidence | | Maternal serum lactate | Not relevant | Not used for fetal assessment | Maternal marker, not fetal | **Tip:** Remember the hierarchy: **CTG first → if non-reassuring, consider scalp blood gas → if still unclear, abandon instrumental delivery and proceed to cesarean.**
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