Q: What is NT?
A: The NT is measured, and when correlated with your age-related risk for Down syndrome, your doctor can calculate a higher or lower risk of carrying a Down syndrome fetus. The measurement of the NT presently identifies about three in four fetuses with Down syndrome.
In one study by Dr. Nicolaides, the following were increased age-adjusted risks of Down syndrome based on the NT measurements at 10-13 weeks:
- 3 mm: 3 times
- 4 mm: 18 times
- 5 mm: 28 times
- 6 mm: 36 times
So, for example, if your age-related risk of Down syndrome is 1 in 365, and the NT measures 5 mm, then the adjusted risk is 28 times higher or 1 in 13.