## Mechanism of Ovulation Suppression in Combined OCPs **Key Point:** Combined oral contraceptive pills (containing both estrogen and progestin) prevent ovulation primarily through **negative feedback suppression of gonadotropins**. ### How It Works 1. **Estrogen component** suppresses FSH secretion by negative feedback on the anterior pituitary and hypothalamus 2. **Progestin component** suppresses LH surge by negative feedback, preventing the midcycle LH peak that triggers ovulation 3. Together, they create a **hypogonadotropic state** that prevents follicular development and ovulation ### Secondary Contraceptive Mechanisms While ovulation suppression is the PRIMARY mechanism, OCPs also work through: | Mechanism | Contribution | Timing | |-----------|--------------|--------| | Cervical mucus thickening | Secondary | Continuous | | Endometrial atrophy | Tertiary | Chronic use | | Altered tubal motility | Minor | Continuous | **High-Yield:** The **estrogen component is critical for ovulation suppression**; progestin-only pills (POPs) do not reliably prevent ovulation and work mainly through cervical mucus and endometrial changes. **Clinical Pearl:** This is why even a 7-day pill-free interval allows FSH to rise and follicular development to begin — the negative feedback is removed, allowing the hypothalamic-pituitary-ovarian axis to recover. [cite:Park 26e Ch 3]
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