A woman at 8 weeks gestation opts for medical abortion. She is given mifepristone 200 mg orally, followed 24–48 hours later by misoprostol 800 mcg sublingually. Which mechanism makes mifepristone the sensitizing agent in this regimen?

• A Mifepristone increases uterine sensitivity to oxytocin by upregulating oxytocin receptors
• B Mifepristone directly stimulates uterine contractions via PGE2 pathway
• C Mifepristone inhibits hCG production, thereby destabilizing the corpus luteum
• D Mifepristone blocks progesterone receptors, causing decidual necrosis and increasing uterine sensitivity to prostaglandins ✓

Explanation

Mifepristone is a competitive progesterone receptor antagonist that blocks progesterone's trophic effect on the decidua, causing decidual necrosis and detachment of the conceptus. Concurrently, it upregulates prostaglandin receptors (PGE and PGF) in the myometrium, dramatically increasing uterine contractile sensitivity to subsequently administered misoprostol. It also has antiglucocorticoid activity but does not directly cause contractions or inhibit hCG.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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