Mifepristone works in medical abortion primarily by:
- A Competitively binding progesterone receptors, blocking progesterone's decidual and anti-contractile effects ✓
- B Directly stimulating uterine oxytocin receptors
- C Inhibiting HCG production from the trophoblast
- D Activating prostaglandin E2 receptors directly
Correct answer: A. Competitively binding progesterone receptors, blocking progesterone's decidual and anti-contractile effects
Explanation
Mifepristone (RU-486) is a synthetic steroid that competitively antagonizes the progesterone receptor with 3–5× greater affinity than progesterone itself. This blocks progesterone-maintained decidual support for the pregnancy, softens and dilates the cervix, sensitizes the myometrium to prostaglandins (by upregulating prostaglandin receptors), and promotes trophoblast detachment. It does not directly stimulate oxytocin receptors or inhibit hCG. When followed 24–48 hours later by misoprostol (prostaglandin E1 analogue), complete expulsion rates exceed 95% in the first trimester.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
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Written and medically reviewed by the StethoPrep medical team.