A 36-week primigravida presents with transverse lie on ultrasound. She is hemodynamically stable with intact membranes and no contraindications to external cephalic version (ECV). What is the drug of choice to facilitate successful ECV?

Explanation

## External Cephalic Version (ECV) — Tocolytic Choice ### Mechanism of ECV Facilitation Successful ECV requires uterine relaxation to reduce resistance during manual rotation of the fetus. Tocolytics suppress myometrial contractions, increasing the likelihood of version success and reducing maternal/fetal trauma. ### Drug Comparison for ECV | Agent | Class | Onset | Duration | Efficacy in ECV | Adverse Effects | | --- | --- | --- | --- | --- | --- | | **Terbutaline** | β₂-agonist | 5–10 min (IV/SC) | 2–4 hrs | **Gold standard** — 60–70% success | Tachycardia, tremor, hyperglycemia | | Nifedipine | CCB | 10–20 min (PO) | 4–6 hrs | Good efficacy (55–65%) | Headache, flushing; slower onset | | Magnesium sulfate | NMDA antagonist | 30–60 min | 4–6 hrs | Moderate efficacy | Flushing, weakness; slow onset | | Indomethacin | NSAID | Variable | 4–6 hrs | Poor tocolytic effect | GI upset, renal effects; not preferred | **Key Point:** Terbutaline (0.25 mg SC or 0.125 mg IV) is the **first-line tocolytic for ECV** due to rapid onset (5–10 minutes), short duration (allowing safe labor induction if needed), and highest success rates in clinical trials. **High-Yield:** ECV success rates improve from ~40% (no tocolytic) to 60–70% (with terbutaline). This translates to fewer cesarean sections for malpresentation. **Clinical Pearl:** Terbutaline is preferred over nifedipine in the ECV setting because its rapid onset allows the obstetrician to attempt version while uterine relaxation is optimal; nifedipine's slower onset and longer duration make it less ideal for this acute intervention. **Warning:** Do NOT use indomethacin for ECV — it has poor tocolytic properties and increases risk of ductus arteriosus constriction if used near term. ### Contraindications to ECV - Ruptured membranes - Vaginal bleeding or placenta previa - Previous cesarean with classical incision - Abnormal fetal heart rate tracing - Multiple gestation (relative) [cite:Williams Obstetrics 25e Ch 28]