How is a hydatidiform (H) mole diagnosed in pregnancy?

Diagnosis of Hydatidiform Mole in Pregnancy

The diagnosis of a hydatidiform mole in pregnancy requires ultrasound examination, serum hCG measurement, and histologic examination of tissue obtained through suction curettage. 1

Initial Diagnostic Approach

Clinical Suspicion

• Vaginal bleeding is the most common presenting symptom, typically occurring between 6-16 weeks of gestation 1
• Earlier diagnosis is now common due to routine ultrasound screening in early pregnancy 1, 2
• Additional signs may include uterine enlargement beyond expected gestational age, preeclampsia, hyperemesis, anemia, and theca lutein ovarian cysts 1

Essential Diagnostic Tests

• Ultrasound (US): Primary imaging modality for initial diagnosis 1

  • First trimester complete moles typically appear as complex, echogenic intrauterine masses containing many small cystic spaces 2
  • Uterine artery Doppler may be used as an optional adjunct 1

• Serum hCG measurement: Typically elevated beyond the expected level for gestational age 1

  • Important to use an assay that can detect all forms of beta hCG 1
  • False-positive results can occur; when hCG results don't match clinical picture, use a different assay 1

• Blood group determination: Required for potential anti-D immunization in Rh-negative women 1

• Chest X-ray (CXR): Recommended if clinical suspicion of metastases or as baseline 1

• Thyroid function tests: Should be performed if hyperthyroidism is suspected 1

Definitive Diagnosis

Tissue Sampling and Histologic Examination

• Suction curettage under anesthesia is the standard procedure for both diagnosis and treatment 1

  • Blood should be available pre-operatively due to risk of significant blood loss 1
  • Rhesus-negative women should receive anti-D immunization 1
  • Cervical ripening can be considered, though consensus on this is lacking 1

• Histologic examination is the definitive method for diagnosis and classification 1

  • Differentiates between complete hydatidiform mole (CHM) and partial hydatidiform mole (PHM) 1, 3
  • Review by an experienced pathologist is recommended as differentiation can be difficult 1
  • Ancillary techniques including genetic analysis may be necessary to confirm the type of molar pregnancy 1, 4

Post-Evacuation Assessment

• US or hysteroscopy should be performed to ensure complete evacuation 1
• Reference pathology review (with or without ancillary techniques) in a GTD center within 2 weeks is considered best practice 1

Follow-up After Diagnosis

• Serum hCG monitoring at least once every 2 weeks until normalization 1
• Use hCG assay type as advised by the GTD center 1
• For CHM: Monthly hCG for up to 6 months after normalization 1
• For PHM: One more normal serum hCG over 1 month after initial normalization 1
• Reliable contraception is necessary until follow-up is complete 5, 6

Common Pitfalls and Caveats

• Early molar pregnancies may not demonstrate the classical clinical or pathological features, making diagnosis challenging 3, 2
• Some hCG assays may fail to detect all isoforms/fragments or significantly under or over-read certain isoforms, leading to false-negative or false-positive results 1
• When a false positive is suspected, assessment of urine hCG can be helpful as cross-reactive molecules rarely get into the urine 1
• Differentiation between hydropic miscarriage, CHM, and PHM can be difficult and may require expert pathological review 1, 3
• Medication that induces uterine contractions should be avoided during evacuation 6