What is the continuing pregnancy rate after APR?

Since 2012, three case series (Delgado 20121; Garratt 20172; Delgado 20183) and two clinical trials (Creinin 20204; Turner 20235) have studied Abortion Pill Rescue (APR) in humans. The five studies investigated the continuing pregnancy rate (CPR) for mifepristone followed by progesterone using 12 different progesterone dosing and delivery regimens. The chart on this page presents the results of these studies.

The vertical axis shows the continuing pregnancy rate reported by each study, broken down by dosing and delivery regime. For instance, Delgado 2018e shows the CPR for oral administration of micronized progesterone, whereas Delgado 2018f shows the CPR using intramuscular injection (refer to Dataset 2 for details). The horizontal red line indicates the ≤25% CPR for mifepristone alone for ≤49 days gestation. See “What is the continuing pregnancy rate after mifepristone alone?” for an analysis of how we arrived at the ≤25% number.

Clinical Trials versus Observational Studies

The underlying data for this chart comes from two types of evidence: clinical trials and observational studies. Many clinicians and researchers consider randomized clinical trials (RCT) the “gold standard” for medical evidence. Well-designed RCTs exhibit internal validity. A study with internal validity has medical evidence that supports a strong claim about cause and effect. RCTs use randomization, which minimizes the risk of bias by confounding.6 RCT results may have limited generalizability if the study sample does not represent the general population.7 RCTs are often expensive to perform, resulting in a small sample size. RCTs may be unethical for questions such as when equipoise does not exist.

There has been an increase in the use of evidence obtained from observational studies.8 Well-designed observational studies can offer superior external validity compared to RCTs. A survey with external validity has medical evidence that applies to the general population.9 However, observational studies do not randomize interventions and may exhibit poor internal validity due to the risk of confounding bias.10 Observational studies are rarely unethical to perform, tend to have larger sample sizes, and are often less costly than RCTs.

Many systematic reviews have found no difference in treatment effect estimates between RCTs and observational studies. For instance, in 2024, Toews et al. compared data from 2869 RCTs (N=3,882,115) and 3924 observational studies (N=19,499,970). The authors found “no difference or a very small difference between effect estimates from RCTs and observational studies.”11 In 2014, Anglemyer et al. analyzed the results from over 1000 RCTs and over 1000 observational studies. They concluded, “There is little evidence for significant effect estimate differences between observational studies and RCTs, regardless of specific observational study design, heterogeneity, or inclusion of studies of pharmacological interventions.”12

NEXT: Refer to the Studies page to view APR research collections. Refer to the Spotlight page for the latest APR news.

  1. Delgado, George, and Mary L. Davenport. “Progesterone Use to Reverse the Effects of Mifepristone.” Annals of Pharmacotherapy, vol. 46, no. 12, Dec. 2012, pp. 1723–1723. DOI.org (Crossref), https://doi.org/10.1345/aph.1R252. ↩︎
  2. Garratt, Deborah, and Joseph V. Turner. “Progesterone for Preventing Pregnancy Termination after Initiation of Medical Abortion with Mifepristone.” The European Journal of Contraception & Reproductive Health Care, vol. 22, no. 6, Nov. 2017, pp. 472–75. DOI.org (Crossref), https://doi.org/10.1080/13625187.2017.1412424. ↩︎
  3. Delgado, George, et al. “A Case Series Detailing the Successful Reversal of the Effects of Mifepristone Using Progesterone.” Issues in Law & Medicine, vol. 33, no. 1, 2018, pp. 21–31. https://pubmed.ncbi.nlm.nih.gov/30831017/ ↩︎
  4. Creinin, Mitchell D., et al. “Mifepristone Antagonization With Progesterone to Prevent Medical Abortion: A Randomized Controlled Trial.” Obstetrics & Gynecology, vol. 135, no. 1, Jan. 2020, p. 158. journals.lww.com, https://doi.org/10.1097/AOG.0000000000003620. ↩︎
  5. Turner, Joseph V., Deborah Garratt, Lucas A. McLindon, Anna Barwick, and M. Joy Spark. 2023. “Progesterone after Mifepristone: A Pilot Prospective Single Arm Clinical Trial for Women Who Have Changed Their Mind after Commencing Medical Abortion.” Journal of Obstetrics and Gynaecology Research, November, jog.15826. https://doi.org/10.1111/jog.15826. ↩︎
  6. Gaudino, Mario, Emilia Bagiella, Helena L. Chang, and Paul Kurlansky. 2022. Randomized Trials, Observational Studies, and the Illusive Search for the Source of Truth. The Journal of Thoracic and Cardiovascular Surgery 163 (2): 757–62. https://doi.org/10.1016/j.jtcvs.2020.10.120. ↩︎
  7. Bosdriesz, Jizzo R., Vianda S. Stel, Merel van Diepen, Yvette Meuleman, Friedo W. Dekker, Carmine Zoccali, and Kitty J. Jager. 2020. Evidence‐based Medicine—When Observational Studies Are Better than Randomized Controlled Trials. Nephrology (Carlton, Vic.) 25 (10): 737–43. https://doi.org/10.1111/nep.13742. ↩︎
  8. Hong, Yoon Duk, Jeroen P. Jansen, John Guerino, Marc L. Berger, William Crown, Wim G. Goettsch, C. Daniel Mullins, Richard J. Willke, and Lucinda S. Orsini. 2021. Comparative Effectiveness and Safety of Pharmaceuticals Assessed in Observational Studies Compared with Randomized Controlled Trials. BMC Medicine 19 (1): 307. https://doi.org/10.1186/s12916-021-02176-1. ↩︎
  9. Booth, C. M., and I. F. Tannock. 2014. Randomised Controlled Trials and Population-Based Observational Research: Partners in the Evolution of Medical Evidence. British Journal of Cancer 110 (3): 551–55. https://doi.org/10.1038/bjc.2013.725. ↩︎
  10. Bosdriesz, Jizzo R., Vianda S. Stel, Merel van Diepen, Yvette Meuleman, Friedo W. Dekker, Carmine Zoccali, and Kitty J. Jager. 2020. Evidence‐based Medicine—When Observational Studies Are Better than Randomized Controlled Trials. Nephrology (Carlton, Vic.) 25 (10): 737–43. https://doi.org/10.1111/nep.13742. ↩︎
  11. Toews, Ingrid, Andrew Anglemyer, John LZ Nyirenda, Dima Alsaid, Sara Balduzzi, Kathrin Grummich, Lukas Schwingshackl, and Lisa Bero. 2024. Healthcare Outcomes Assessed with Observational Study Designs Compared with Those Assessed in Randomized Trials: A Meta‐epidemiological Study. Cochrane Database of Systematic Reviews, no. 1. https://doi.org/10.1002/14651858.MR000034.pub3 ↩︎
  12. Anglemyer, Andrew, Hacsi T. Horvath, and Lisa Bero. 2014. “Healthcare Outcomes Assessed with Observational Study Designs Compared with Those Assessed in Randomized Trials.” Cochrane Database of Systematic Reviews, no. 4. https://doi.org/10.1002/14651858.MR000034.pub2. ↩︎