A 28-year-old woman from rural India presents with vaginal bleeding and lower abdominal pain 6 weeks after a missed period. Ultrasound shows a heterogeneous intrauterine mass with multiple small cystic spaces ('bunch of grapes' appearance) and markedly elevated β-hCG (>100,000 mIU/mL). What is the most common histological type of gestational trophoblastic disease in this patient?

## Gestational Trophoblastic Disease: Histological Classification **Key Point:** Complete hydatidiform mole (complete molar pregnancy) is the most common form of gestational trophoblastic disease, accounting for approximately 80–90% of all GTD cases. ### Clinical Presentation of Complete Mole - Vaginal bleeding in first or second trimester - Markedly elevated β-hCG (often >100,000 mIU/mL) - Uterine size larger than expected for gestational age - Characteristic ultrasound: heterogeneous mass with multiple small cystic spaces ('bunch of grapes') - Absent fetal parts (no fetal tissue in complete mole) ### Epidemiology and Pathology | Feature | Complete Mole | Partial Mole | Invasive Mole | Choriocarcinoma | |---------|---------------|--------------|---------------|------------------| | **Frequency** | 80–90% of GTD | 10–15% of GTD | <5% of GTD | 1–2% of GTD | | **Karyotype** | 46,XX or 46,YY (diploid) | 69,XXY or 69,XXX (triploid) | Invades myometrium | No chorionic villi | | **Fetal tissue** | Absent | Present | Present | Absent | | **β-hCG level** | Very high (>100,000) | Moderately elevated | Variable | Very high | | **Malignant potential** | 15–20% | 1–5% | High | Nearly 100% | **High-Yield:** Complete molar pregnancy arises from fertilization of an empty egg by a single sperm (which duplicates) or two sperm — resulting in 46,XX or 46,YY karyotype with purely paternal DNA. ### Why Other Options Are Less Common **Invasive mole** (~5% of GTD): - Occurs when molar tissue invades the myometrium and beyond - Develops in 10–15% of patients after evacuation of a complete mole - Less frequent as a primary presentation than uncomplicated mole **Choriocarcinoma** (1–2% of GTD): - Malignant tumour with no chorionic villi - Can arise after any pregnancy (mole, abortion, normal pregnancy, ectopic) - Accounts for only 1–2% of primary GTD diagnoses - More common as a sequela of molar pregnancy than as de novo disease **Placental site trophoblastic tumour** (<1% of GTD): - Rare, arises from intermediate trophoblast - Often follows normal pregnancy - Extremely uncommon in the setting described **Clinical Pearl:** Any woman with first-trimester bleeding, markedly elevated β-hCG, and a 'bunch of grapes' ultrasound pattern should be presumed to have a complete molar pregnancy until proven otherwise. The diagnosis is confirmed by histology after suction evacuation. **Tip:** In NEET PG exams, when asked "most common GTD," the answer is always **complete hydatidiform mole** unless the stem explicitly specifies malignant GTD (in which case choriocarcinoma becomes relevant).