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

Nuchal translucency (NT) measurement is a critically important screening test for fetal structural abnormalities during early pregnancy. The normal NT range varies by maternal age group: for pregnant women under 35 years old, the NT value should be less than 2.5 mm; for those aged 35 years or older, the normal upper limit is 3.0 mm. If the gestational age is between 14 and 22 weeks, an NT value ≥6 mm is considered abnormal. Therefore, interpretation of NT results must take both gestational age and maternal age into account. An increased NT measurement does not definitively indicate fetal abnormalities; rather, it signifies an elevated risk of such abnormalities.