The Rotterdam criteria (2003) for PCOS diagnosis require 2 out of 3 features. A woman has oligomenorrhoea and elevated serum androgens but a normal ultrasound. She asks about the mechanism by which elevated LH (characteristic of PCOS) contributes to anovulation. Which best describes this mechanism?

• A Elevated LH directly suppresses GnRH release, preventing FSH surge and follicular maturation
• B Elevated LH causes excessive corpus luteum formation, creating persistent progesterone that suppresses ovulation
• C Elevated LH stimulates insulin growth factor-1 in granulosa cells, causing follicular atresia
• D Elevated LH stimulates premature luteinisation of follicles before they reach mature size, and promotes theca cell androgen production that inhibits follicular maturation ✓

Explanation

In PCOS, tonic elevated LH (from an accelerated GnRH pulse frequency due to impaired progesterone negative feedback) causes two key effects on anovulation: first, LH stimulates theca cells to produce excess androgens (testosterone and androstenedione), which in excess inhibit granulosa cell aromatase activity and prevent follicular maturation; second, chronic LH elevation causes premature luteinisation of small antral follicles before they reach dominant follicle size, arresting them as cystic structures. FSH levels are relatively low due to negative feedback from elevated oestrone (from peripheral aromatisation), maintaining LH:FSH ratio >2:1.

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

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