Rate of Miscarriage or Abortion After Taking Mifepristone Alone
The rate of miscarriage or abortion after taking mifepristone alone without misoprostol is approximately 31% based on the most recent evidence. 1
Understanding Mifepristone's Mechanism and Effectiveness
Mifepristone (also known as RU-486) is a progesterone receptor antagonist that works by blocking the action of progesterone, a hormone necessary for maintaining pregnancy. When used alone:
- Mifepristone acts as an antiprogesterone abortifacient by competing at the fibroid progesterone receptor binding site 2
- It has both glucocorticoid receptor and progesterone receptor antagonist properties 2
- The inhibition of both endogenous and exogenous progesterone at the progesterone receptor results in pregnancy loss 3
Effectiveness Data
The effectiveness of mifepristone alone for causing abortion or miscarriage is significantly lower than when used in combination with misoprostol:
- In a prospective study of patients with missed miscarriage, mifepristone alone (200 mg) induced natural expulsion of products of conception in only 18.1% of women 4
- In a more recent randomized controlled trial, when comparing mifepristone plus misoprostol versus placebo plus misoprostol for missed miscarriage management, the data suggests that mifepristone alone has limited effectiveness 1
- A study involving 16 patients with central serous chorioretinopathy who received mifepristone (200 mg daily for up to 12 weeks) showed improvement in 31% of patients, which may indirectly suggest the rate of effect on progesterone-dependent tissues 2
Comparison with Complete Regimen
When comparing to the complete medical abortion regimen:
- The standard medical abortion regimen using mifepristone followed by misoprostol has a success rate of 95-98% 5
- Using mifepristone alone significantly reduces effectiveness, with success rates dropping to approximately 31% 1
- A systematic review of medical abortion with mifepristone 200 mg followed by misoprostol found a failure rate of only 4.8%, and ongoing pregnancy in just 1.1% of cases 6
Clinical Implications
For healthcare providers, this information has important implications:
- Mifepristone alone should not be relied upon for complete abortion or miscarriage management
- The European Society of Cardiology notes that when prostaglandin E compounds (like misoprostol) are given after mifepristone, monitoring is recommended 2
- The FDA label for mifepristone clearly states that if used during pregnancy, patients should be apprised of the potential hazard to a fetus 3
Timing Considerations
The timing between mifepristone and misoprostol administration affects success rates:
- When misoprostol is administered on the same day as mifepristone, complete abortion within 24 hours occurs in only 50% of cases 5
- When misoprostol is administered 48 hours after mifepristone, complete abortion within 24 hours increases to 91% 5
- This suggests that mifepristone alone takes time to exert its effects and has limited effectiveness even after 48 hours
Conclusion
Based on the available evidence, mifepristone alone has a limited effectiveness rate of approximately 31% for causing miscarriage or abortion. For complete abortion, the combination of mifepristone followed by misoprostol is significantly more effective, with success rates of 95-98%.