Table 1.
Factors that affect fetal fraction of circulating DNA.
| Positive correlation | No correlation |
|---|---|
| Maternal weight (29–31, 33) | Maternal age (29, 32) |
| Gestational age (29, 33) | Nuchal translucency measurement (31, 32) |
| Maternal ethnicity (32) | Maternal ethnicity (29, 31) |
| Serum PaPP-A and free βhCG levels (31, 32)a | Plasma/serum storage time (31) |
| Fetal karyotype (↓ in trisomy 21, ↓ in trisomy 18) (29, 32) | Fetal sex (31, 32) |
| Maternal smoking (32) | Maternal smoking (31) |
a
PaPP-A, pregnancy-associated plasma protein A; βhCG, β human chorionic gonadotropin.