Exceeding how many millimeters of nuchal translucency is considered abnormal?

• A. 2 mm
• B. 3 mm
• C. 4 mm
• D. 5 mm

Answer: (B)

Nuchal translucency is the fluid-filled space at the back of the fetal neck measured in the first trimester to assess risk for chromosomal abnormalities. When this thickness exceeds about 3 millimeters, it is considered abnormal because larger NT measurements correlate with a higher likelihood of chromosomal conditions such as trisomy 21 and other congenital issues, prompting further evaluation.

The measurement is performed in the mid-sagittal view between 11 and 14 weeks, using calipers on the inner edges of the translucency, with the fetus in a neutral position. Values around 2 mm are typically within the normal range for many gestational ages, whereas 4 or 5 mm would be notably elevated, but the standard clinical threshold used for flagging an abnormal result is 3 mm.