Triploidity (Asymmetric)
Trisomy 18. Trisomy 13, Trisomy 21 - Down Syndrome (Symmetric)
Symmetry is defined based on HC/AC (Fetal Biometry (US))
| Type | HC/AC | Shows up in GA | Common Causes |
|---|---|---|---|
| Type I: Symmetric (30%) | HC = AC | Early | Trisomies (13, 18, 21); TORCH Infection |
| Type II: Asymmetric (70%) | HC > AC (brain spared) | Late | Triploidy, Placental Insufficiency |