Complete molar pregnancy (complete hydatidiform mole) is the most common form of gestational trophoblastic disease, characterized by hydropic degeneration of all chorionic villi without fetal tissue. Incidence is ~1/1000 pregnancies; more common in Southeast Asia. Genetically androgenetic — 46,XX (most common) or 46,XY karyotype with all chromosomes of paternal origin (empty ovum + sperm duplication or dispermic fertilization). β-hCG levels are markedly elevated (>100,000 mIU/mL). The 'snowstorm' pattern on US is pathognomonic — heterogeneous endometrial mass filled with multiple small cystic areas without fetal parts. Bilateral theca lutein cysts accompany in 15-25% of cases. Complete mole carries 15-20% risk of malignant transformation (invasive mole, choriocarcinoma) → post-evacuation β-hCG monitoring is mandatory.
Age Range
15-50
Peak Age
25
Gender
Female predominant
Prevalence
Rare
Complete molar pregnancy results from fertilization of an empty ovum (enucleated) by a sperm — all genetic material is paternal (androgenesis). In 46,XX karyotype, single sperm duplication occurs; in 46,XY, fertilization by two different sperm (dispermy). Without maternal genome, normal embryogenesis cannot occur but trophoblastic proliferation is excessive → all villi show hydropic (fluid-filled) degeneration. Hydropic villi form 1-30 mm diameter, grape-like vesicles. On US, these vesicles create the 'snowstorm' pattern: multiple small anechoic-hypoechoic cystic areas (hydropic villi) surrounded by echogenic trophoblastic tissue. Excessive trophoblastic proliferation causes high β-hCG production → β-hCG stimulates ovarian theca cells → bilateral theca lutein cysts (multiple, large, simple cysts). Malignant transformation risk arises from abnormal invasive potential of trophoblasts.
Heterogeneous echogenic mass filled with multiple small cystic areas in the uterine cavity — no fetal parts — pathognomonic ultrasonographic finding of complete molar pregnancy. Cystic areas represent hydropic villi.
A heterogeneous echogenic mass filling the uterine cavity is seen — containing multiple small anechoic-hypoechoic cystic areas (1-30 mm hydropic villi). This appearance is described as 'snowstorm' or 'grape cluster'. NO fetal structures, yolk sac, or amniotic membrane are present. In the first trimester, villi may be small and the pattern may appear more homogeneous, less cystic — cystic areas become more prominent in later weeks.
Report Sentence
A heterogeneous echogenic mass containing multiple small cystic areas is seen in the uterine cavity with 'snowstorm' pattern, consistent with complete molar pregnancy.
Multiple, large (generally >6 cm), thin-walled simple cysts are seen in both ovaries — bilateral theca lutein cysts. Cysts may be multiloculated and sometimes fill the entire ovary. They form from luteinization and cystic enlargement of theca cells due to excessive β-hCG stimulation. Cysts spontaneously regress within weeks to months after molar evacuation as β-hCG declines.
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Multiple large, thin-walled cysts are seen in both ovaries, representing bilateral theca lutein cysts — consistent with gestational trophoblastic disease.
Molar tissue appears markedly hypervascular on color Doppler — diffusely increased vascularity with low-resistance arterial flow. Neovascularization from trophoblastic proliferation gives much more intense Doppler signal compared to normal early pregnancy. In the presence of myometrial invasion (invasive mole), increased myometrial vascularity is detected.
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Molar tissue is markedly hypervascular on color Doppler with low-resistance arterial flow.
On T2-weighted MRI, multiple high-signal cystic areas (hydropic villi) are seen in the uterine cavity with low-to-intermediate signal solid trophoblastic tissue between them. MRI is superior to US in evaluating myometrial invasion depth — critical for diagnosing invasive mole. Junctional zone integrity and myometrial thickness are clearly evaluated on T2 sections.
Report Sentence
Multiple hyperintense cystic areas with intervening solid trophoblastic tissue are seen in the uterine cavity on T2-weighted MRI, consistent with complete molar pregnancy.
CT is not typically the primary diagnostic tool but is used for complications (pulmonary metastasis, theca lutein cyst rupture) or staging. On contrast-enhanced CT, a heterogeneously enhancing mass is seen in the uterine cavity — showing prominent enhancement in arterial phase due to intense vascularity. Chest CT evaluates pulmonary metastases — choriocarcinoma shows hematogenous spread.
Report Sentence
A heterogeneously enhancing mass is seen in the uterine cavity on CT, consistent with gestational trophoblastic disease.
Criteria
Detected on first-trimester US, villi still small
Distinct Features
Snowstorm pattern may not be prominent — more homogeneous echogenic mass, may be confused with missed abortion, β-hCG correlation critical
Criteria
Second-trimester US, prominent hydropic villi
Distinct Features
Typical snowstorm pattern, large theca lutein cysts, uterus large for gestational age, increased complication risk
Criteria
β-hCG plateaued or rising after evacuation, myometrial invasion present
Distinct Features
Hypervascular mass in myometrium on US/MRI, increased Doppler signal, β-hCG not declining, requires chemotherapy
Distinguishing Feature
Partial mole shows 'Swiss cheese' pattern WITH ABNORMAL fetal parts; complete mole has NO fetal parts with snowstorm pattern
Distinguishing Feature
Retained products show post-delivery/miscarriage endometrial thickening; complete mole is diagnosed pre-evacuation with extremely high β-hCG
Distinguishing Feature
SCH shows normal intrauterine pregnancy + subchorionic collection; complete mole has no fetal structures with snowstorm pattern
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAfter diagnosis of complete molar pregnancy, evacuation is performed by suction curettage. Post-evacuation β-hCG monitoring is mandatory: weekly β-hCG measurement, monthly monitoring after 3 consecutive normal values, total 6-12 months. If β-hCG plateaus or rises → gestational trophoblastic neoplasia (GTN) diagnosis → chemotherapy. Pregnancy is contraindicated until β-hCG monitoring is completed. Complete mole has 15-20% risk of malignant transformation. Theca lutein cysts regress spontaneously — no surgical intervention needed (except torsion).
Complete mole is the most common form of gestational trophoblastic disease. Treatment is suction curettage. GTN (invasive mole or choriocarcinoma) develops in 15-20% of cases — β-hCG monitoring is mandatory. At least 6 months of contraception is recommended after β-hCG normalizes. Prophylactic chemotherapy is debated in high-risk groups.