Clomiphene citrate is used for ovulation induction in WHO Group II anovulation. It is a selective estrogen receptor modulator (SERM) with predominantly anti-estrogenic effects at the hypothalamic level. What is its primary mechanism of inducing ovulation?

• A Direct stimulation of ovarian granulosa cells to produce estradiol
• B Suppression of LH pulsatility to prevent premature luteinization
• C Blockade of estrogen receptors at the hypothalamus, reducing negative feedback and increasing FSH/LH secretion ✓
• D Aromatase inhibition leading to reduced peripheral estrogen production

Explanation

Clomiphene citrate is a SERM that competitively blocks estrogen receptors at the hypothalamus and pituitary, reducing negative feedback. This increases GnRH pulse frequency and FSH/LH secretion, stimulating follicular development. Option D describes letrozole, not clomiphene. Option A is incorrect as clomiphene has no direct ovarian stimulatory effect. Option B is the opposite of clomiphene's action.

Reference: Williams Gynecology, 4th ed.

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