Which of the following is the most common type of gestational trophoblastic disease?

Explanation

## Classification of Gestational Trophoblastic Disease **Key Point:** Complete molar pregnancy (hydatidiform mole) accounts for approximately 80% of all gestational trophoblastic diseases, making it the most common type. ### Epidemiology and Incidence | GTD Type | Frequency | Key Feature | | --- | --- | --- | | Complete molar pregnancy | ~80% | 46,XX or 46,XY (diploid, all paternal) | | Partial molar pregnancy | ~15% | Triploid (69,XXY or 69,XXX) | | Invasive mole | ~3-5% | Invades myometrium | | Choriocarcinoma | ~1-2% | Highly malignant, no chorionic villi | ### Complete Molar Pregnancy **High-Yield:** Complete moles result from fertilization of an empty egg by a single sperm that duplicates (46,XX) or by two sperm (46,XY). There is no fetal tissue, only trophoblastic tissue. **Clinical Pearl:** Presents with: - Vaginal bleeding in first or second trimester - Markedly elevated β-hCG (often >100,000 mIU/mL) - Uterus larger than expected for dates - Theca lutein cysts on ovaries (due to high hCG) - Characteristic "bunch of grapes" appearance on ultrasound ### Partial Molar Pregnancy - Results from fertilization of a normal egg by two sperm (diandry) - Contains some fetal tissue with abnormal development - Lower β-hCG levels than complete moles - Lower malignant potential (~1-5% risk of persistent GTD) **Warning:** Do not confuse partial moles with complete moles — partial moles have fetal tissue present, while complete moles do not. [cite:Robbins 10e Ch 22]