Table 4 Prevalence of common chromosome abnormalities [trisomies (T) 21, 18 and 13 and sex chromosome abnormalities] and atypical (or other) abnormalities in screen-positive pregnancies with or without any of the four risk factors, including a risk of T21 > 1 in 100,a nuchal translucency (NT) ≥ 3.5 mm, a low pregnancy associated plasma protein A (PAPP-A) < 0.2 multiple of medians, and a high risk for both trisomy 21 and trisomy 18
| Â | Common abnormalities | Atypical abnormalities |
|---|---|---|
No risk factors | 1.1% | 0.6% |
One or more of the risk factors | 11.5% | 1.7% |