A non-inferiority study of outpatient mifepristone-misoprostol medical abortion at 64-70 days and 71-77 days of gestation.

Objectives: This open-label non-inferiority study assessed efficacy of a common outpatient medical abortion regimen among people with pregnancies 64-70 days and 71-77 days of gestation.

Study Design: We defined non-inferiority by a 6% margin of method success. People with intrauterine pregnancies 64-77 days' gestational age by abdominal ultrasound seeking medical abortion at one of eight clinics and met eligibility criteria were offered participation. Consenting participants took mifepristone 200 mg followed 24-48 h later by misoprostol 800 mcg buccally, and returned after one week for provider evaluation and abdominal ultrasound to determine abortion status. Participants recorded medication use, pregnancy expulsion, daily bleeding and pain scores until the one-week follow up. Clinic staff interviewed participants prior to study discharge to assess acceptability.

Results: Seven hundred and nineteen participants were enrolled, 393 and 326 in the respective groups. Successful expulsion without surgical intervention was achieved in 92.3% of the earlier gestational age group and 86.7% of the later group (difference in proportions 5.6%, 1-sided 95% CI 9.6). Ongoing pregnancy accounted for 3.6% and 8.7% (p = 0.007) of outcomes, respectively. Participants in the 71-77 day group reported nausea and weakness more frequently. Pain, bleeding and acceptability measures between groups were similar.

Conclusion: Although the success rate at 71-77 days of gestation was within the non-inferiority margin, we cannot rule out that it is statistically worse than in the previous gestational week. Significantly more ongoing pregnancies in the later group raise concerns about using the regimen at 71-77 days.