NTNB scan and dual marker testn in Rohini, An NT/NB scan, or Nuchal Translucency/Nasal Bone scan, is a prenatal ultrasound that assesses the health of a fetus. It's usually performed between 11 and 14 weeks of pregnancy. What it checks for Chromosomal abnormalities: The scan checks for the risk of Down syndrome, Edwards syndrome, and Patau syndrome. Structural abnormalities: The scan checks for structural abnormalities like spina bifida. Heart defects: The scan checks for major congenital heart problems. Nasal bone: The scan checks if the fetus has developed a nasal bone.