A 25-year-old woman at 8 weeks requests medical termination of pregnancy. She is given mifepristone 200 mg orally followed 48 hours later by misoprostol 800 mcg vaginally. The mechanism by which mifepristone sensitizes the uterus to misoprostol involves:

• A Mifepristone competitively blocks glucocorticoid receptors, reducing cortisol-mediated cervical ripening inhibition
• B Mifepristone blocks progesterone receptors, increasing prostaglandin sensitivity and upregulating oxytocin receptors while softening the cervix ✓
• C Mifepristone inhibits 5-alpha reductase, increasing estradiol-progesterone ratio
• D Mifepristone stimulates oxytocin release from the posterior pituitary directly

Explanation

Mifepristone is a 19-norsteroid antiprogestogen that competitively antagonizes progesterone receptors (as well as glucocorticoid receptors at high doses). By blocking progesterone's pregnancy-maintaining effects on the uterus and decidua, mifepristone upregulates prostaglandin receptors and oxytocin receptors in the myometrium, primes the cervix for ripening via decidual prostaglandin release, and creates a state in which the uterus is highly sensitive to subsequent prostaglandin (misoprostol) stimulation. This sequential regimen has 95–98% efficacy for first trimester termination. The glucocorticoid receptor blockade at standard doses (200 mg) is clinically insignificant.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.