Normally, Nuchal Translucency should be :

Fetal nuchal translucency is the maximum thickness of the subcutaneous translucent area between the skin and soft tissue that overlies the fetal spine in the sagittal plane. It is measured between 11- 14 weeks of gestation. Up to 3 mm is considered normal. NT > 3 mm is a marker for aneuploidys. like trisomy 21.