If the
maternal age is advanced following are taken to be pointers towards chromosomal abnormality like Down's which is trisomy 21-- Sonographic markers include thickness of the nuchal fold, cardiac abnormalities, duodenal atresia, shortened femur, shortened humerus, renal pyelectasis, absence of the nasal bone , a hyperechogenic bowel, and a choroid plexus cyst. None of these markers are specific, and false-positive rates have been reported.