A 28-year-old woman with regular menstrual cycles presents for fertility counselling. Which of the following is the most common cause of anovulation in women of reproductive age?

Explanation

## Most Common Cause of Anovulation ### Epidemiology of Anovulation **Key Point:** Polycystic ovary syndrome (PCOS) is the most common endocrine disorder causing anovulation in women of reproductive age, affecting 5–10% of women globally. ### PCOS: Pathophysiology of Anovulation | Feature | Mechanism | Effect on Ovulation | |---------|-----------|---------------------| | Insulin resistance | Hyperinsulinemia → excess androgen production | Follicle maturation arrest | | Elevated LH:FSH ratio | Abnormal GnRH pulsatility | Premature luteinization, no ovulation | | Abnormal follicle development | Multiple small follicles, no dominant follicle | Anovulation | | Chronic anovulation | Unopposed estrogen → endometrial hyperplasia | Irregular/absent menses | ### Why PCOS is Most Common 1. **Prevalence:** 5–10% of reproductive-age women 2. **Mechanism:** Multifactorial (genetic + environmental + metabolic) 3. **Clinical presentation:** Irregular cycles, infertility, hirsutism, acne 4. **Diagnosis:** Rotterdam criteria (2 of 3: oligo/anovulation, hyperandrogenism, polycystic ovaries on imaging) **High-Yield:** PCOS is the leading cause of anovulatory infertility in women of reproductive age. ### Comparison with Other Causes | Cause | Prevalence | Mechanism | Key Feature | |-------|-----------|-----------|-------------| | **PCOS** | **5–10%** | **Hyperandrogenism + insulin resistance** | **Most common** | | Hyperprolactinemia | 0.4–1% | Dopamine antagonism → ↓ GnRH | Galactorrhea, amenorrhea | | Thyroid dysfunction | 1–2% (in general population) | ↑ TRH → ↑ prolactin | Amenorrhea + systemic symptoms | | Premature ovarian failure | 0.1–0.3% | Autoimmune/genetic ovarian destruction | Age < 40, ↑ FSH | **Clinical Pearl:** Although hyperprolactinemia and thyroid dysfunction are important causes of anovulation, they are far less common than PCOS in the reproductive-age population. **Mnemonic:** **PCOS** — **P**olycystic **C**auses **O**vulation **S**uppression (most common)