Introduction
The Fetal Medicine Foundation promotes screening for Down syndrome at 11-13+6 weeks by Nuchal Translucency or a combination of nuchal translucency and maternal serum biochemistry.
Extensive research has now established that screening by nuchal translucency
can detect about 80% of affected fetuses for a screen positive rate of
5%. The combination of nuchal translucency and maternal serum free ß-hCG
and PAPP-A improves the detection to 90%. There is now evidence that the
detection rate can increase to more than 95% by also examining the nasal
bone, facial angle, tricuspid flow and ductus venosus flow. Alternatively,
with the inclusion of these new markers the detection rate of 90% can be
achieved with a reduction in the false positive rate from 5% to 2.5%.
The Fetal Medicine Foundation advocates that effective screening requires:
- Appropriate counselling - see Patient Information section
- Measurement of nuchal translucency and the other markers by appropriately trained sonographers - see Certification in the 11-13+6 Weeks Scan and Registered Centres
- Measurement of maternal serum free ß-hCG and PAPP-A by laboratories that can demonstrate good quality assurance performance - see Registered Laboratories.
- A risk calculation program that uses an algorithm based on scientific evidence - see Registered Software.