A 28-year-old woman from Delhi presents with irregular menstrual cycles for 3 years, hirsutism, and acne. On examination, BMI is 26 kg/m², and there is mild clitoromegaly. Serum testosterone is 0.8 ng/mL (normal <0.7 ng/mL). What is the investigation of choice to confirm the diagnosis of PCOD?

Explanation

## Diagnosis of PCOD — Role of Imaging **Key Point:** Transvaginal ultrasound (TVS) is the gold standard imaging modality for diagnosing PCOD and is part of the Rotterdam criteria. ### Rotterdam Criteria for PCOD Diagnosis A woman must meet ≥2 of 3 criteria (after excluding other causes): | Criterion | Details | | --- | --- | | **Oligo/anovulation** | Irregular or absent periods | | **Clinical/biochemical hyperandrogenism** | Hirsutism, acne, elevated androgens | | **Polycystic ovaries on imaging** | ≥12 follicles (2–9 mm) per ovary OR ovarian volume ≥10 cm³ | ### Why TVS is the Investigation of Choice 1. **Direct visualization** of ovarian morphology — the hallmark of PCOD is multiple small follicles arranged peripherally around a hyperechoic stroma. 2. **High sensitivity and specificity** — TVS is more accurate than transabdominal ultrasound for detecting the polycystic pattern. 3. **Non-invasive, reproducible, and cost-effective** — no radiation, no contrast, can be repeated. 4. **Meets diagnostic criteria** — imaging findings are a mandatory component of the Rotterdam criteria. **Clinical Pearl:** The presence of ≥12 follicles (2–9 mm diameter) in at least one ovary on TVS, combined with clinical/biochemical features, confirms PCOD. A single ovary meeting criteria is sufficient. **High-Yield:** TVS is preferred over transabdominal ultrasound because the higher frequency probe provides better resolution of small follicles and ovarian stroma. ### Why Other Investigations Are Supportive, Not Diagnostic - **Serum LH:FSH ratio** — elevated (typically >3:1) in ~70% of PCOD patients, but not diagnostic on its own; many normal women have elevated ratios, and many PCOD patients have normal ratios. - **Free androgen index** — reflects hyperandrogenism but does not diagnose the ovarian morphology; useful for confirming biochemical hyperandrogenism. - **Pelvic MRI** — reserved for specific indications (e.g., suspicion of adrenal tumour, complex cysts); not first-line for PCOD diagnosis due to cost and lack of additional diagnostic value over TVS.