Normal Organ should be observed under Ultrasound
Normal thickness for NT (< 3 mm)
Increased in NT thickness (> 3mm) & absence of Nasal Bone.
Although NT scan is a sensitive screening scan to pick up cases of thickened NT as well as the presence of the nasal bone, it's not a definitive tool to give final diagnosis, and the final diagnosis often required an extra step called amniocentesis (to extract the amniotic fluid to access the DNA to run specific testing.)
Sources: http://www.fetalmedicine.com/fmf/training-certification/certificates-of-competence/11-13-week-scan/nuchal/