What is the normal range for NT (nuchal translucency), in millimeters?
Mar 17, 2022
Source: Cainiu Health
Dr. Zhang Lu
Introduction
The normal nuchal translucency (NT) measurement is less than 2.5 mm—or alternatively, less than 3.0 mm. NT ultrasound is performed between 11 and 13⁺⁶ weeks of gestation to assess the thickness of the fetal nuchal translucency. An NT measurement exceeding 0.3 cm indicates an increased risk of fetal chromosomal abnormalities. Referral to a higher-level hospital for genetic counseling is recommended, and prenatal diagnosis may be necessary.
NT, or nuchal translucency, refers to the maximum thickness between the skin and the underlying soft tissue at the level of the fetal cervical spine in a sagittal ultrasound view. NT measurements correlate with chromosomal abnormalities and fetal cardiac malformations. So, what is the normal NT range in millimeters? Let’s explore this together.
What is the normal NT range (in mm)?
The normal NT value varies with gestational age—increasing as pregnancy progresses. Most clinical centers define the upper limit of normal NT as <2.5 mm or <3.0 mm. NT measurement is performed via ultrasound between 11 and 13⁺⁶ weeks’ gestation. If the nuchal translucency thickness exceeds 3.0 mm (0.3 cm), it suggests an increased risk for fetal chromosomal abnormalities. In such cases, referral to a higher-level hospital for genetic counseling and, if indicated, prenatal diagnosis is recommended.
1. Due to individual variation, some healthy fetuses naturally have relatively more subcutaneous fluid, which may affect NT measurement accuracy. A slightly increased NT does not necessarily indicate fetal abnormality. Therefore, when NT >2.5 mm, close attention is warranted, and further prenatal counseling is advised. Based on the specific clinical scenario, the physician will determine whether additional diagnostic tests—including chorionic villus sampling (CVS), amniocentesis, or later fetal echocardiography—are necessary.
2. During pregnancy, regular antenatal check-ups are essential to enable timely identification and appropriate management of any issues, thereby minimizing adverse effects on fetal growth and development.
The above addresses the question: “What is the normal NT range (in mm)?” If an NT scan reveals a measurement exceeding the normal range, further structural anomaly screening is indicated—such as amniocentesis or chorionic villus biopsy—to assess for Down syndrome or other genetic conditions. We hope this information is helpful to you.
