NT value of 1.7mm is normal. NT value refers to the thickness of the nuchal translucency layer of the fetus and is a screening indicator for congenital stupidity. It is usually measured by ultrasound at 11-13 weeks + 6 days. Nowadays, NT value is usually less than 3mm in clinical practice, while 2.5mm is the alert value. If the NT value is greater than 3mm, a possible chromosomal abnormality is considered and amniocentesis is recommended. If NT value is less than 2.5mm, it is normal range and no special treatment is needed. 2.5mm-3mm intermediate need to do non-invasive DNA test, and it is recommended to measure the thickness again by ultrasound at 17-20 weeks, it should be less than 6mm, if it is more than 6mm, consider that there may be chromosomal abnormality and recommend amniocentesis test.