NT / NB SCAN is a type of ultrasound done in pregnancy to see nuchal translucency and nasal bones. Nuchal translucency is skin fold at nape of baby which has fluid and Doctor take thickness of this fold. NORMALLY nuchal translucency should be less than 3.5 mm . Nasal bone is length of nasal bone, it is absent or reduced in length in chromosomal anomalies as Down syndrome, Patau syndrome abd Edward syndrome. NT, nasal bone are two parameters to detect fetal anomalies . It is done between 11-14 we