Misoprostol Dosing for 4-Month (Second Trimester) Pregnancy Termination
For second trimester pregnancy termination at 4 months (approximately 13-20 weeks), use vaginal misoprostol 400 mcg every 3 hours up to 5 doses, which is the most effective regimen when mifepristone is unavailable. 1
Optimal Dosing Protocol
Vaginal administration is significantly superior to oral administration for mid-trimester termination, with a mean induction-to-delivery interval of 17.5 hours (vaginal) versus 33 hours (oral), and 93% of women delivering within 24 hours with vaginal administration compared to only 19% with oral. 2, 3
Recommended Regimen (Misoprostol Alone):
- Initial dose: 400 mcg vaginally
- Subsequent doses: 400 mcg vaginally every 3 hours
- Maximum: Up to 5 doses 1
- Alternative protocol: 800 mcg initial vaginal dose, followed by 400 mcg orally every 3 hours (maximum 3 additional doses) 4
Enhanced Regimen (With Mifepristone - Preferred When Available):
- Mifepristone: 200 mg orally first
- Wait: 36-48 hours
- Misoprostol: 800 mcg vaginally, then 400 mcg vaginally every 3 hours (maximum 4 additional doses) 5
- This combination achieves 97.9% abortion rate within 24 hours and median induction-to-abortion interval of only 6.7 hours 5
Critical Safety Considerations
Absolute contraindication: Never use misoprostol in women with previous cesarean delivery due to 13% uterine rupture risk, substantially higher than oxytocin (1.1%) or prostaglandin E2 (2%). 6, 7
Monitoring Requirements:
- Continuous fetal heart rate and uterine activity monitoring from 30 minutes to 2 hours after each administration 7, 8
- Monitor for uterine hyperstimulation, which occurs less frequently with vaginal versus oral routes 7
Expected Outcomes and Management
Efficacy:
- Vaginal misoprostol alone: 85-93% delivery within 24 hours 2, 3
- With mifepristone pretreatment: 97.9% within 24 hours, 99.5% within 36 hours 5
- Failure rate: Approximately 1-2% may require surgical intervention 4, 5
Common Side Effects:
- Gastrointestinal symptoms (nausea/vomiting): 22% 4
- Fever/chills: 20-25% 4, 3
- Abdominal cramping (expected therapeutic effect) 1
- Bleeding (expected) 1
Complications Requiring Intervention:
- Incomplete abortion or retained placenta: 5-20% may require manual removal or curettage 4, 5
- Infection: Rare but monitor for febrile morbidity 3
- Uterine rupture: Extremely rare with appropriate dosing and no prior cesarean 1
Common Pitfalls to Avoid
- Do not use oral route as first-line - vaginal administration is significantly more effective with shorter induction times 2, 3
- Do not exceed recommended dosing frequency - higher doses increase side effects without improving efficacy 7, 1
- Do not use in women with prior cesarean delivery - unacceptably high rupture risk 6, 7
- Do not use beyond 30 weeks without dose reduction - reduce to 50-100 mcg vaginally every 3 hours due to increased uterine rupture risk 4
Cost and Practical Advantages
Misoprostol is significantly more cost-effective at $0.36-$1.20 per 100 mcg tablet compared to dinoprostone ($65-$165), and remains stable at room temperature without refrigeration requirements. 7