First Test to Order After Molar D&C with Persistent β-hCG
Order a pelvic Doppler ultrasound as the first investigation for persistent β-hCG after molar pregnancy evacuation. 1
Rationale for Pelvic Doppler Ultrasound as Initial Test
The ESMO guidelines explicitly state that for patients developing gestational trophoblastic neoplasia (GTN) post-molar pregnancy, "information to determine therapy can be obtained from the clinical history, examination, measurement of serum hCG and a Doppler pelvic ultrasound" as the primary staging investigation. 1
What the Pelvic Doppler Ultrasound Provides
- Confirms absence of new pregnancy (critical to rule out before considering chemotherapy) 1
- Measures uterine size and volume to assess disease burden 1
- Evaluates spread of disease within the pelvis 1
- Assesses vascularity via Doppler pulsatility index, which is an independent prognostic factor for resistance to single-agent methotrexate therapy 1
Algorithmic Approach to Staging Workup
Step 1: Pelvic Doppler Ultrasound (First Test)
Obtain this immediately when persistent β-hCG is confirmed (plateaued for 4 consecutive values over 3 weeks, rising >10% for 3 consecutive values over 2 weeks, or persisting 6 months post-evacuation). 1, 2, 3
Step 2: Chest X-Ray (Second Test)
Since pulmonary metastases are the most common site of spread, obtain a chest radiograph next. 1, 2, 3
Step 3: Conditional Advanced Imaging
- If chest X-ray is normal: No further imaging needed, as CT chest discovery of micrometastases (seen in ~40% of patients) does not influence outcome or management 1
- If chest X-ray shows lesions >1 cm: Proceed with MRI brain and CT chest/abdomen to exclude brain or liver metastases, which would significantly alter management 1
Critical Pitfalls to Avoid
Never perform re-biopsy to confirm malignant transformation, as this carries significant risk of life-threatening hemorrhage. 2, 3 The diagnosis of post-molar GTN is made based on β-hCG criteria and imaging findings, not tissue diagnosis.
Never start chemotherapy without confirming absence of new pregnancy via ultrasound, as this would be catastrophic for a viable pregnancy. 1, 4
Never order CT chest as the initial imaging if chest X-ray hasn't been done first, as micrometastases detected only on CT don't change management in low-risk disease. 1
Why Not Other Tests First?
While serial β-hCG monitoring is essential for detecting persistent disease 2, 3, 5, 6, the question assumes persistent β-hCG has already been established. At that point, the staging workup begins with pelvic Doppler ultrasound to guide treatment decisions. 1
Laboratory tests (CBC, metabolic panel, thyroid function) are important for pre-treatment assessment but don't provide the anatomic and prognostic information needed to determine whether single-agent versus multi-agent chemotherapy is required. 2, 3