## Uterine Relaxation in Vaginal Breech Delivery ### Clinical Context Vaginal breech delivery is now rare in most centers due to the Term Breech Trial (2000), but in carefully selected multiparous women with frank/complete breech, informed consent, and experienced providers, it may be attempted. During the second stage (delivery of the body and head), uterine relaxation is critical to prevent entrapment of the fetal head and allow controlled delivery of the shoulders and head. ### Agent Selection for Acute Uterine Relaxation | Agent | Mechanism | Onset | Duration | Use in Breech Delivery | Notes | | --- | --- | --- | --- | --- | --- | | **Glyceryl Trinitrate (GTN)** | Nitric oxide donor; direct smooth muscle relaxation | **Immediate** (IV/SL) | 5–10 min | **Gold standard** for acute uterine relaxation | Rapid, profound relaxation; allows head delivery | | Terbutaline | β₂-agonist | 5–10 min | 2–4 hrs | Slower than GTN; less ideal for acute need | Better for ECV; tachycardia risk | | Hydralazine | Arteriolar vasodilator | 10–20 min (IV) | 4–6 hrs | Not used for uterine relaxation | Primarily for hypertension management | | Labetalol | α/β-blocker | 5–10 min (IV) | 4–6 hrs | Not used for uterine relaxation | Primarily for hypertension management | **Key Point:** GTN (0.5–1 mg IV bolus or 400–800 μg sublingual spray) produces **immediate, profound uterine relaxation** lasting 5–10 minutes — ideal for the acute need to deliver an entrapped fetal head during vaginal breech delivery. **High-Yield:** GTN is preferred over terbutaline in vaginal breech delivery because: 1. **Faster onset** (seconds to 1–2 min vs. 5–10 min) 2. **More profound relaxation** (complete arrest of contractions) 3. **Shorter duration** (5–10 min vs. 2–4 hrs) — allows rapid redosing if needed 4. **No systemic side effects** (no tachycardia, no hyperglycemia) **Clinical Pearl:** GTN is also used for acute uterine relaxation in other obstetric emergencies: retained placenta, uterine inversion, and manual removal of retained products of conception. It is the agent of choice whenever **immediate, short-lived uterine relaxation** is needed. **Warning:** Terbutaline, while useful for ECV, is too slow for the acute crisis of an entrapped fetal head during vaginal breech delivery. Hydralazine and labetalol are vasodilators for blood pressure control, not uterotonic agents. ### Vaginal Breech Delivery — Selection Criteria (ACOG/FIGO) - Frank or complete breech (not footling) - Estimated fetal weight 2500–3800 g - Adequate maternal pelvis (clinical or imaging assessment) - No hyperextension of fetal head - Experienced provider and immediate cesarean capability - Informed consent and counseling [cite:Williams Obstetrics 25e Ch 28; ACOG Committee Opinion No. 340 (2006, reaffirmed 2019)]
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