Which of the following is the most common cause of abnormal uterine bleeding in reproductive-age women?

Explanation

## Epidemiology of Abnormal Uterine Bleeding **Key Point:** Anovulation secondary to PCOS is the single most common cause of abnormal uterine bleeding in women of reproductive age (15–49 years). ### Frequency Distribution by Age | Age Group | Most Common Cause | Mechanism | |-----------|-------------------|----------| | Adolescence (menarche–19 yrs) | Anovulation (immature HPO axis) | Irregular ovulation, progesterone deficiency | | Reproductive age (20–49 yrs) | **PCOS-related anovulation** | Chronic anovulation, unopposed estrogen | | Perimenopausal (40–55 yrs) | Anovulation (declining ovarian function) | Irregular FSH/LH, variable ovulation | | Postmenopausal (>55 yrs) | Endometrial atrophy, malignancy | Estrogen deficiency, structural pathology | ### Why PCOS Dominates in Reproductive Age 1. **Prevalence**: PCOS affects 8–13% of reproductive-age women (by Rotterdam criteria). 2. **Mechanism**: Chronic anovulation → absent corpus luteum → no progesterone → unopposed estrogen stimulation of endometrium → irregular, heavy, or prolonged bleeding. 3. **Clinical presentation**: Often accompanied by hirsutism, acne, infertility, and metabolic syndrome. **High-Yield:** The PALM-COEIN classification (FIGO 2018) divides AUB causes into Structural (PALM: Polyp, Adenomyosis, Leiomyoma, Malignancy) and Non-structural (COEIN: Coagulopathy, Ovulatory dysfunction, Endometrial, Iatrogenic, Not yet classified). In reproductive-age women, **ovulatory dysfunction (primarily PCOS)** is the most frequent non-structural cause and overall most common etiology. **Clinical Pearl:** A woman with AUB + amenorrhea/oligomenorrhea + clinical or biochemical hyperandrogenism should be screened for PCOS first, before extensive imaging or endometrial biopsy. ## Why Other Options Are Less Common - **Uterine fibroids**: Common structural cause but less frequent overall than PCOS-related anovulation. - **Endometrial polyps**: Structural but less prevalent in younger reproductive-age women. - **Endometrial carcinoma**: Rare in reproductive age; more common in postmenopausal women and those with unopposed estrogen (obesity, PCOS, diabetes).