What will my doctor see on an ultrasound the day after taking Mifeprex (mifepristone)?

What Will Be Visible on Ultrasound the Day After Taking Mifeprex (Mifepristone)

One day after taking Mifeprex (mifepristone), an ultrasound will typically show a pregnancy that appears intact and unchanged from before medication administration, as mifepristone alone does not cause immediate visible changes to the pregnancy on ultrasound imaging.

How Mifepristone Works

• Mifepristone (Mifeprex) is a selective progesterone receptor modulator (SPRM) that blocks progesterone receptors, which are essential for maintaining pregnancy 1
• It was originally discovered during a search for glucocorticoid receptor ligands but was found to be more active as an antiprogesterone abortifacient 1
• Mifepristone was initially developed and commercialized specifically for pregnancy termination 1

Timeline of Effects After Mifepristone Administration

• Within the first 24 hours after taking mifepristone alone:

  • The medication begins to work by blocking progesterone receptors 1
  • This initiates the process of detaching the pregnancy from the uterine lining 1
  • However, these biochemical changes are not immediately visible on ultrasound 2

• Visible effects typically occur only after the second medication (misoprostol) is administered:

  • In standard protocols, misoprostol is administered 24-48 hours after mifepristone 2, 3
  • Expulsion of pregnancy tissue generally begins 1-4 hours after misoprostol administration 4, 5

What the Doctor Will See on Ultrasound

• At 24 hours after mifepristone alone:

  • The gestational sac will likely appear unchanged 2, 6
  • The pregnancy will still be visualized in its original location 3
  • No significant changes in endometrial thickness or appearance 6
  • No evidence of expulsion or detachment of pregnancy tissue 2

• The ultrasound findings will be similar to those before medication administration because:

  • Mifepristone works at the hormonal/cellular level first 1
  • Visible tissue changes and expulsion typically require both medications (mifepristone plus misoprostol) 2, 3, 4

Important Considerations

• Mifepristone alone is only the first step in the medical abortion process 2, 4
• Complete abortion rates with mifepristone alone are much lower than when followed by misoprostol 4
• In clinical studies, approximately 7-9% of women may experience some bleeding after mifepristone but before misoprostol, though this varies 2, 4
• A small percentage (1-5%) may expel pregnancy tissue after mifepristone alone, but this is uncommon 2

Clinical Implications

• If your doctor performs an ultrasound just one day after taking mifepristone:
  • They will likely still see an intact pregnancy 2, 6
  • This does not mean the medication isn't working 1
  • The process of pregnancy termination has begun at the cellular level, but visible changes typically occur after misoprostol administration 2, 4