A Retrospective Cohort Study Evaluating the Effectiveness and Safety of Exogenous Progesterone for the Continuation of Pregnancy After Exposure to Mifepristone.

Background: Reports in the medical literature indicate that there are patients who have initiated medical abortions by taking mifepristone but not misoprostol and have attempted to continue their pregnancies by taking exogenous progesterone. Objective: We sought to evaluate the effectiveness and adverse events of exogenous progesterone taken after mifepristone. Methods: This is a retrospective cohort of consecutive patients who contacted a nonprofit hotline from October 13, 2021 to January 5, 2024. The primary outcome was the rate of continuing pregnancy two weeks after progesterone initiation; secondary outcomes included demographics, progesterone dose and route of administration, and adverse events. A small subset was evaluated for a secondary outcome of gestational age at delivery. Data from a small subset were evaluated for preterm birth and birth defects. Adverse events at two weeks were analyzed. Patients were included if they wanted to attempt to continue their pregnancies after taking mifepristone for medical abortion. Exclusion criteria included never starting progesterone therapy, initiating progesterone more than 72 h after ingesting mifepristone, gestational age at the time of mifepristone ingestion greater than 11 weeks 6 days or undocumented, and surgical or additional medical termination of pregnancy. Results: From 1,466 patients screened, 765 met the inclusion criterion and did not meet exclusion criteria; 418 (55%) had confirmed continuing pregnancies two weeks postinitiation of progesterone therapy. Earlier gestational age at mifepristone use was associated with a decreased likelihood of continuing pregnancy at two weeks (39% vs. 58%, Conclusions: Continuing pregnancy was noted in 55%, superior to the 25% rate documented in the literature for mifepristone alone without intervention. There were a few adverse events associated with progesterone use. These retrospective data suggest the potential benefit of exogenous progesterone administration for patients seeking to continue their pregnancies after taking mifepristone but not misoprostol. Further research, including randomized controlled trials, is needed.