## Pathophysiology of Gestational Trophoblastic Disease **Key Point:** Complete molar pregnancy has a diploid karyotype (46,XX or 46,XY) but is of **purely paternal origin** (androgenetic), NOT biparental. This is the critical distinguishing feature. ### Karyotype and Origin Patterns | Feature | Complete Mole | Partial Mole | |---------|---------------|---------------| | Karyotype | 46,XX (90%) or 46,XY (10%) | Triploid (69,XXY or 69,XXX) | | Genetic Origin | Paternal only (androgenetic) | Biparental (maternal + paternal) | | Fetal Tissue | Absent | Present (abnormal) | | Placental Villi | Hydropic, diffuse | Focal hydropic changes | **High-Yield:** The complete mole arises from fertilization of an empty egg (no maternal DNA) by one or two sperm. Partial moles result from fertilization of a normal egg by two sperm or one diploid sperm, creating triploidy. ### Clinical Features Common to Both - **Markedly elevated β-hCG** (often > 100,000 mIU/mL in complete mole) - **Vaginal bleeding** in first or early second trimester - **Uterine size larger than dates** - **Theca lutein cysts** on ovarian ultrasound - **Hyperemesis gravidarum** (due to high hCG) - **Preeclampsia** in early pregnancy (rare but pathognomonic) ### Malignant Potential **Clinical Pearl:** Invasive mole (chorioadenocarcinoma) can develop from either complete mole (~5–10%) or partial mole (~1–5%). It invades myometrium and can metastasize. Choriocarcinoma (epithelioid trophoblastic tumor) has similar malignant potential from both types. **Mnemonic:** **COMPLETE = Paternal origin** (Complete = Chromosomes from one parent) [cite:Robbins 10e Ch 22]
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