A 32-year-old multiparous woman at 40 weeks gestation is admitted for induction of labor due to gestational diabetes. On examination, the cervix is unfavorable (Bishop score 5). Which drug is the preferred first-line agent for cervical ripening in this patient?

Explanation

## Drug of Choice for Cervical Ripening **Key Point:** Dinoprostone (PGE2) is the preferred prostaglandin for cervical ripening when the cervix is unfavorable (Bishop score <6) prior to labor induction. ### Mechanism & Rationale Dinoprostone is a naturally occurring prostaglandin E2 (PGE2) that: 1. **Softens the cervix** — increases collagen hydration and promotes cervical effacement 2. **Stimulates uterine contractions** — may initiate labor or facilitate transition to active labor 3. **FDA-approved** — specifically indicated for cervical ripening 4. **Reversible** — can be removed (gel formulation) if hyperstimulation occurs 5. **Predictable dosing** — available in gel (0.5 mg) or insert (10 mg sustained-release) formulations ### Dosing & Administration **Dinoprostone Gel (Prepidil®):** - **Dose:** 0.5 mg intracervically - **Frequency:** Every 3–6 hours (maximum 3 doses per 24 hours) - **Advantage:** Can be easily removed if hyperstimulation occurs **Dinoprostone Insert (Cervidil®):** - **Dose:** 10 mg sustained-release insert placed in posterior fornix - **Duration:** Releases 0.3 mg/hour over 12–24 hours - **Advantage:** Single application; can be removed if needed ### Clinical Pearl **High-Yield:** Dinoprostone insert is preferred over gel in many centers because it provides sustained, predictable release and avoids the need for repeated applications. Both formulations can be removed if hyperstimulation (tachysystole with fetal heart rate changes) occurs. ### Comparison of Cervical Ripening Agents | Agent | Type | Onset | Duration | Reversibility | FDA-Approved | Cost | | --- | --- | --- | --- | --- | --- | --- | | **Dinoprostone** | PGE2 | 10–15 min | 2–3 hrs (gel); 12–24 hrs (insert) | Partially reversible (removable) | ✓ Yes | Higher | | Misoprostol | PGE1 analog | 15–30 min | 3–4 hrs | Not reversible | ✗ Off-label | Lower | | Oxytocin | Oxytocin agonist | 3–5 min | 1–2 min | Immediately reversible | ✓ Yes | Low | | Carboprost | PGF2α | 5–10 min | 2–3 hrs | Not reversible | ✗ Not for ripening | — | **Warning:** Oxytocin is NOT appropriate for cervical ripening in unfavorable cervices. It is used only for augmentation in active labor with a favorable cervix or after successful ripening. **Warning:** Ergot alkaloids are contraindicated for cervical ripening and any stage of labor except the third stage (active management of third stage). **Mnemonic:** **PG = Prostaglandin for Ripening** - **PGE2 (Dinoprostone)** — FDA-approved, reversible, preferred - **PGE1 (Misoprostol)** — off-label, cheaper, not reversible - **PGF2α (Carboprost)** — reserved for hemorrhage, not ripening ## Summary Dinoprostone is the first-line FDA-approved agent for cervical ripening in unfavorable cervices. It has predictable pharmacokinetics, can be removed if hyperstimulation occurs, and has the strongest evidence base for safe and effective ripening prior to labor induction. [cite:Williams Obstetrics 26e Ch 21]