"Soft markers are sonographic findings that do not, in themselves, cause any adverse outcomes. However, they are seen more frequently in fetuses with an abnormality. This article addresses the soft markers that are specific to Down syndrome. For a general discussion, please refer to the article on soft markers."
"PAPP-A"
"AFP: lower than in chromosomally normal fetuses"
"Soft markers"
"Structural abnormalities"
"Adjunct features"
Expected headings
"Maternal age"
"Maternal serum screening"
"First trimester"
"Markers"
"Second trimester"
"Markers"
"First trimester"
"Second trimester"
"There is a strong association between the incidence of Down syndrome and maternal age. Background risk based on maternal age is incorporated into both the serum screening-based risk calculations and the calculation of increased risk in the presence of a soft marker in the 2nd trimester (see below)."
"There is evidence that the inclusion of nasal bone measurement improves the specificity of 1st trimester data 5."