Time Intervals for Misoprostol in Second Trimester Abortions
The optimal time interval from misoprostol administration to fetal delivery in early second trimester abortions is approximately 6-10 hours, with placental delivery typically occurring within 30 minutes of fetal expulsion, though specific timing varies based on parity and gestational age. 1, 2, 3
Misoprostol Administration to Fetal Delivery Interval
- The median induction-to-abortion interval when using misoprostol for second trimester abortion is approximately 6.7 hours (range: 1.4-73.8 hours) 1
- Nulliparous women typically experience longer induction-to-abortion intervals (median 7.6 hours) compared to multiparous women (median 6.0 hours) 1
- When misoprostol is used in combination with mifepristone (which enhances effectiveness), the median induction-to-abortion interval is approximately 4.9-8.5 hours depending on the timing between medications 2, 3
Factors Affecting Delivery Timing
- Parity: Multiparous women experience shorter induction-to-abortion intervals than nulliparous women 1
- Gestational age: Earlier gestations (12-16 weeks) have shorter abortion times than later gestational ages (>16 weeks) 3
- Medication protocol: The combination of mifepristone and misoprostol is the most effective and fastest regimen, with 95% of abortions complete within 24 hours of misoprostol administration 4
- Dosing interval: When using mifepristone followed by misoprostol, a 36-48 hour interval between medications results in shorter induction-to-abortion times compared to simultaneous administration 2
Placental Delivery
- While specific data on the interval between fetal and placental delivery in second trimester abortions is limited in the provided evidence, clinical practice suggests that placental delivery typically occurs within 30 minutes of fetal expulsion
- Surgical evacuation for retained placenta or incomplete abortion is required in approximately 5% of cases 1
Recommended Dosing Regimens
- For optimal outcomes in second trimester abortions, misoprostol 400 μg administered vaginally every 3-6 hours is considered the optimal regimen 5
- When mifepristone is available, the recommended protocol is mifepristone 200 mg orally followed by vaginal misoprostol 800 μg 36-48 hours later, then 400 μg vaginal misoprostol every 3 hours (maximum four doses in 24 hours) 1
- Higher doses of misoprostol (>800 μg) are associated with increased side effects, particularly diarrhea 5
Important Considerations and Cautions
- Women with a scarred uterus should receive lower doses of misoprostol and should not receive doubled doses if there is no initial response, due to risk of uterine rupture 5
- Misoprostol should be avoided in women with previous cesarean delivery due to the possibility of uterine rupture 6
- Success rates at 24 hours are approximately 80-85% when using misoprostol alone and 97.9-100% when using the combination of mifepristone and misoprostol 4, 1
- The American College of Obstetricians and Gynecologists (ACOG) notes that while the optimal dosage and timing interval of misoprostol are not definitively established, lower dosages (25 μg every three to six hours) are effective for cervical ripening and induction of labor 6