What is the karyotype of a complete molar pregnancy?

Explanation

## Karyotype and Genetic Origin in Complete Molar Pregnancy **Key Point:** Complete molar pregnancy has a diploid karyotype (46,XX or 46,XY) that is entirely of paternal origin, with no maternal genetic contribution. ### Mechanism of Formation 1. An ovum loses its maternal chromosomes (becomes "empty") 2. A single sperm duplicates its chromosomes → 46,XX complete mole 3. OR two sperm fertilize the empty ovum → 46,XY complete mole 4. Result: All DNA is paternal; no fetal tissue develops **High-Yield:** The absence of maternal DNA in complete moles explains why there is no fetal tissue — only trophoblastic tissue proliferates. ### Comparison: Complete vs. Partial Molar Pregnancy | Feature | Complete Mole | Partial Mole | | --- | --- | --- | | Karyotype | 46,XX or 46,XY (diploid) | 69,XXY or 69,XXX (triploid) | | Genetic origin | All paternal (biparental disomy) | Diandry (2 paternal, 1 maternal) | | Fetal tissue | Absent | Present (abnormal) | | Trophoblastic tissue | Hydropic, excessive | Focal | | β-hCG level | Very high (>100,000) | Moderately elevated | | Malignant potential | ~15-20% | ~1-5% | **Clinical Pearl:** The diploid karyotype in complete moles is why they are sometimes called "diploid moles," distinguishing them from the triploid partial moles. **Mnemonic:** COMPLETE = Chromosome Complete (diploid, all paternal) [cite:Park 26e Ch 10] [cite:Park 26e Ch 10]