What is the normal range for nuchal translucency (NT) measurement?

NT (Nuchal Translucency) refers to the measurement, via ultrasound, of the thickness of the fluid-filled space at the back of the fetal neck in pregnant women between 11 and 14 weeks of gestation. What is the normal NT value range?

What constitutes a normal NT value?

Under normal circumstances, an NT value < 3 mm is considered within the normal range; values ≥ 3 mm generally indicate an abnormality. The NT scan assesses embryonic development based on the thickness of the nuchal translucency. An elevated NT measurement—i.e., above the normal threshold—is associated with a significantly increased risk of Down syndrome (trisomy 21) and other chromosomal abnormalities. Moreover, the higher the NT value, the greater the risk. Therefore, NT measurement serves as an important early indicator for Down syndrome and chromosomal anomalies. The optimal timing for NT screening is between 11 weeks and 13 weeks + 6 days of gestation; it is essential to undergo this examination at a hospital during this window and receive appropriate management if indicated.

Values exceeding this threshold confirm high-risk status and are associated with increased rates of fetal chromosomal abnormalities and structural malformations. In such cases, amniocentesis is typically performed during the second trimester to establish a definitive diagnosis. If chromosomal abnormalities are confirmed by amniocentesis, termination of pregnancy in the second trimester should be considered. Additionally, second-trimester ultrasound screening for fetal structural anomalies must be intensified; if severe malformations are detected, second-trimester termination of pregnancy may also be indicated.

The NT measurement reflects early embryonic development; if abnormal, both first-trimester and second-trimester screening tests for Down syndrome must be performed. We hope this information is helpful to you!