Importance
Misoprostol alone regimens for abortion may be more effective than previously thought; real-world effectiveness data on misoprostol alone regimens can provide critical evidence.

Objective
To estimate the effectiveness of medication abortion using misoprostol alone among a sample of participants self-managing their abortion with support from safe abortion hotlines and accompaniment groups.

Design
Prospective observational cohort study of callers to safe abortion hotlines and accompaniment groups; participants recruited prior to starting their medication abortion and completed a baseline and two follow-up surveys. Recruitment started July 31, 2019 and concluded October 1, 2020.

Setting
Three safe abortion hotlines/accompaniment groups in Argentina, Nigeria, and Southeast Asia.

Participants
Callers 13 years or older with no contraindications to medication abortion who contacted above groups for support in a new self-managed abortion process.

Intervention
Observational study of participants who self-managed their abortion using misoprostol alone.

Main Outcome
The primary outcome was method effectiveness, classified as having a complete abortion without need for surgical intervention by last follow-
up. Secondary outcomes included method safety, measured by self-report of experiencing warning signs (heavy bleeding, pain, fever, discharge) and medical treatment (blood transfusion, intravenous fluids, overnight hospital stay)indicative of a potential complication. Additional outcomes included length of bleeding and cramping, time to expulsion, and experience of side effects.

Results
Of the 1352 enrolled participants, 637 (591 [92.8%] from Nigeria, 384 [60.2%] aged 20-29, 522 [82.0%] pregnancy durations below 9 weeks) used misoprostol alone regimens for abortion and are included in this analysis. At last follow-up, 625 participants (98.1%, 95% CI: 96.7 to 98.9) had a
complete abortion without surgical intervention. Potential adverse events were reported by 6 participants (0.9%, 0.4% to 2.1%). Most participants experienced bleeding for less than one week (median: 4 days, IQR: 3 to 6 days), and expelled their pregnancy within 24 hours of starting their abortion process (median: 12 hours, IQR: 9 to 15 hours). Common side effects included nausea (52.6%), fever (36.4%), and diarrhea (28.4%).

Conclusions
Misoprostol alone is a highly effective method of pregnancy termination; future research should explore strategies to maximize effectiveness in clinical and non-clinical settings.