Laboratory Tests for Suspected Molar Pregnancy
When molar pregnancy is suspected, obtain a quantitative serum beta-hCG, complete blood count with platelets, comprehensive metabolic panel including liver and renal function tests, thyroid function tests (TSH and free T4), blood type and screen, and a chest X-ray. 1
Essential Initial Laboratory Workup
The complete workup for suspected molar pregnancy includes the following tests 1:
Quantitative serum beta-hCG: This is the single most important laboratory test, as molar pregnancies typically present with markedly elevated hCG levels, often exceeding 100,000 mIU/mL in complete moles 1, 2. The hCG level helps establish baseline values for post-evacuation monitoring and serves as a risk factor for developing gestational trophoblastic neoplasia 1.
Complete blood count (CBC) with platelets: Essential for detecting anemia from vaginal bleeding and assessing platelet count before surgical evacuation 1. Mean platelet volume (MPV) >8.55 fL has 84.6% sensitivity for predicting persistent disease, while platelet-to-lymphocyte ratio >102.25 has 86.6% sensitivity 3.
Comprehensive metabolic panel: Liver enzymes (AST, ALT) are elevated in 40-50% of patients with hyperemesis gravidarum associated with molar pregnancy 4. Renal function tests identify electrolyte imbalances from excessive vomiting 4, 1.
Thyroid function tests (TSH, free T4): Hyperthyroidism occurs in molar pregnancies due to hCG cross-reactivity with TSH receptors, particularly when hCG levels are markedly elevated 4, 1.
Blood type and screen: Required before surgical evacuation to prepare for potential hemorrhage and to determine Rho(D) immunoglobulin administration needs 1.
Chest X-ray: Screens for pulmonary metastases, which can occur even at initial presentation, though more commonly develops in post-molar gestational trophoblastic neoplasia 1.
Ultrasound Correlation
While not a laboratory test, transvaginal ultrasound is performed concurrently and shows characteristic findings: a heterogeneous intrauterine mass with multiple cystic spaces ("snowstorm" appearance) in complete moles, or focal cystic placental changes with possible fetal tissue in partial moles 4, 1. The combination of ultrasound findings with elevated hCG establishes the presumptive diagnosis 5, 6.
Post-Evacuation Monitoring Protocol
After surgical evacuation, the critical laboratory follow-up involves 1, 7:
- Serial quantitative hCG every 1-2 weeks until three consecutive normal values are obtained 1
- Monthly hCG for 6 months after normalization for complete moles 1, 7
- One additional normal hCG value after normalization for partial moles 7, 2
Red Flags Requiring Additional Workup
If hCG plateaus for 4 consecutive values over 3 weeks, rises >10% for 3 consecutive values over 2 weeks, or persists for 6 months post-evacuation, this indicates post-molar gestational trophoblastic neoplasia requiring staging workup with pelvic Doppler ultrasound, repeat chest X-ray, and potentially CT/MRI imaging 1.
Common Pitfalls to Avoid
Do not rely on urine pregnancy tests alone, as they lack the quantitative precision needed for diagnosis and monitoring 2. Avoid using different laboratories for serial hCG measurements, as assay variability can confound interpretation 2. Do not delay obtaining thyroid function tests in patients with severe hyperemesis, as thyroid storm is a potential complication 4. Never perform re-biopsy to confirm malignant transformation due to hemorrhage risk 1.