In a patient with rising quantitative β‑hCG after dilation and curettage for a molar pregnancy, which initial imaging study is preferred—chest X‑ray or pelvic ultrasound—and why, according to clinical guidelines?

Pelvic Ultrasound First, Then Chest X-Ray

In a patient with rising quantitative β-hCG after dilation and curettage for molar pregnancy, perform a pelvic Doppler ultrasound immediately as the first imaging study, followed by chest X-ray as the second test. 1, 2

Why Pelvic Ultrasound Comes First

The pelvic Doppler ultrasound serves multiple critical diagnostic and safety functions that must be addressed before any other imaging:

• Excludes a new intrauterine pregnancy before initiating chemotherapy, which is mandatory to avoid harming a viable gestation 2
• Quantifies uterine disease burden by measuring uterine size and volume, providing objective assessment of local tumor extent 1, 2
• Evaluates intrapelvic spread of gestational trophoblastic neoplasia (GTN), supplying essential anatomic staging information 2
• Assesses uterine arterial vascularity using Doppler pulsatility index, which serves as an independent prognostic marker for resistance to single-agent methotrexate therapy and guides treatment selection 2

Why Chest X-Ray Comes Second

After the pelvic ultrasound establishes local disease status:

• Chest X-ray screens for pulmonary metastases, which represent the most common site of GTN metastatic spread 1, 2, 3
• If the chest X-ray is normal, no further imaging is required in low-risk disease; although chest CT can detect micrometastases in approximately 40% of patients, these findings do not alter outcome or management decisions 2
• If chest X-ray shows lesions >1 cm, immediately proceed to brain MRI and chest/abdomen CT to rule out brain or liver metastases, which would substantially change therapeutic strategy and risk stratification 2, 3

Critical Pitfall to Avoid

• Never order chest CT as the initial imaging study before obtaining a chest X-ray; micrometastatic disease detected only on CT does not influence management in low-risk GTN and represents unnecessary radiation exposure and cost 2
• Never start chemotherapy without first confirming absence of a new pregnancy by ultrasound, as this could jeopardize a viable gestation 2

Complete Pre-Treatment Workup Sequence

After pelvic ultrasound and chest X-ray, the NCCN recommends completing the staging evaluation with:

• Complete blood count with platelet count 1
• Liver, renal, and thyroid function tests 1
• Blood type and screen for potential transfusion 1

This algorithmic approach ensures patient safety, provides comprehensive staging information, and guides appropriate risk stratification using the FIGO scoring system (score ≤6 = low-risk requiring single-agent chemotherapy; score ≥7 = high-risk requiring multi-agent EMA-CO) 1, 3, 4.