A 28-year-old woman presents with vaginal bleeding and lower abdominal pain 8 weeks after a missed period. On examination, the uterus is larger than expected for gestational age. Serum β-hCG is markedly elevated at 450,000 mIU/mL. Which is the investigation of choice to confirm the diagnosis and assess for metastases?

## Diagnosis and Staging of Molar Pregnancy **Key Point:** Transvaginal ultrasound is the primary imaging modality for diagnosis of molar pregnancy, showing the characteristic 'bunch of grapes' appearance or heterogeneous echotexture. However, in gestational trophoblastic disease (GTD), staging for metastases is mandatory because of the risk of malignant transformation. **High-Yield:** The investigation sequence for suspected molar pregnancy is: 1. Transvaginal ultrasound (diagnostic) 2. Chest X-ray (detect pulmonary metastases — most common site) 3. CT abdomen/pelvis (assess for hepatic and abdominal metastases) **Clinical Pearl:** Markedly elevated β-hCG (>100,000 mIU/mL) is associated with complete molar pregnancy and increased risk of persistent gestational trophoblastic neoplasia (PGTN). Metastatic disease occurs in 15–20% of complete moles. ### Why This Combination? | Investigation | Purpose | Sensitivity | |---|---|---| | Transvaginal ultrasound | Diagnose molar pregnancy | >95% for molar pregnancy | | Chest X-ray | Screen for pulmonary metastases | 80–90% | | CT abdomen/pelvis | Detect hepatic, renal, ovarian metastases | >95% | **Mnemonic:** **SCOUT** — Screen, Confirm, Organize staging, Ultrasound transvaginal, Then metastatic workup. **Warning:** Serum progesterone is not diagnostic of GTD. Diagnostic curettage is therapeutic (evacuation) but not diagnostic imaging. MRI alone is inadequate for metastatic staging.