A 28-year-old woman presents to the emergency department 18 hours after unprotected intercourse during her fertile window. She is otherwise healthy with regular 28-day cycles and no contraindications to hormonal therapy. She is concerned about pregnancy and requests emergency contraception. Which of the following is the most appropriate first-line agent and timing for maximum efficacy?

Explanation

## Emergency Contraception: Levonorgestrel vs Alternatives **Key Point:** Levonorgestrel is the first-line emergency contraceptive in most settings, particularly when access and cost are considerations. It is most effective within 72 hours of unprotected intercourse, with efficacy decreasing with time. ### Mechanism of Action Levonorgestrel works primarily by: 1. Inhibiting or delaying ovulation (most effective if given before LH surge) 2. Altering cervical mucus consistency 3. Potentially affecting endometrial receptivity (minor role) ### Efficacy Timeline | Agent | Timing Window | Efficacy | Notes | |-------|---------------|----------|-------| | **Levonorgestrel 1.5 mg** | ≤72 hours | 60–90% (best <24 hrs) | First-line, OTC availability, affordable | | **Ulipristal acetate 30 mg** | ≤120 hours | 65–95% (superior 72–120 hrs) | Selective progesterone receptor modulator, more effective in later window | | **Mifepristone 10 mg** | ≤72 hours | 85–90% | Not widely available in India; abortifacient at higher doses | | **Copper IUD** | ≤5 days | >99% | Most effective; requires insertion; not suitable for all | **High-Yield:** At 18 hours post-intercourse, levonorgestrel remains highly effective (>85% pregnancy prevention) and is the standard first-line choice in India due to availability, cost, and established safety profile. ### Why Levonorgestrel at This Timepoint? - Patient is well within the 72-hour window - Single-dose regimen improves compliance - No absolute contraindications mentioned - Cost and accessibility favor levonorgestrel in Indian healthcare settings **Clinical Pearl:** Efficacy is inversely proportional to time elapsed. A patient at 18 hours has significantly better outcomes than one at 70 hours. This patient should be counseled that efficacy decreases after 72 hours, and she should take the dose immediately. **Warning:** Levonorgestrel is NOT effective if ovulation has already occurred. It does not terminate an established pregnancy (hCG-positive). [cite:Park 26e Ch 8]