Nuchal Translucency Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Steven Wooding
Based on research by
Chung JH, Yang JH, Song MJ, Cho JY, Lee YH, Park SY, Moon MJ, Lim HJ, Choi JS, Kim JO, Shin JS, Ahn HK, Han JY, Kim MY, Choi KH, Ryu HM The distribution of fetal nuchal translucency thickness in normal Korean fetuses Journal of Korean Medical Science (February 2004)See 2 more sources
Salman Guraya S. The associations of nuchal translucency and fetal abnormalities; significance and implications Journal of Clinical and Diagnostic Research (May 2013)Sharifzadeh M, Adibi A, Kazemi K, Hovsepian S. Normal reference range of fetal nuchal translucency thickness in pregnant women in the first trimester, one center study. Journal of Research in Medical Sciences (October 2015)
Last updated: Sep 05, 2022

Our nuchal translucency calculator finds the percentile of the nuchal fold thickness and compares it with the nuchal translucency measurement chart. This calculation allows us to estimate the risk of the genetic disorders of a given pregnancy.

The simple NT scan risk calculator on your left is just the beginning of the journey – read on to find out more about what is a normal NT scan, discover the nuchal translucency normal range at 13 weeks and learn about the meaning of abnormal CRL and NT values. 🚼

What is the nuchal translucency test?

Nuchal translucency (NT) is a measure of a thickness of a fold located on the fetuses' neck. This fold's greater thickness is connected to the greater prevalence of genetic disorders, fetal death, and its major abnormalities. NT is one of the 1st trimester screening methods.

We perform a nuchal translucency test during the ultrasound examination in the pregnancy's first trimester. During your visit, your doctor will:

  • Measure the NT and compare it to nuchal translucency normal range;
  • Find the crown-rump length and the gestational age of a fetus;
  • Check other important parts of the fetuses' body, such as the presence or absence of a nasal bone;
  • Note and assess the mother's age; and
  • Perform blood tests and assess the level of pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (HCG).

💡 A proper evaluation of a nuchal fold requires both the CRL and NT calculators – we should always evaluate the nuchal translucency according to the gestational age and the crown-rump length of a fetus.

💡 A normal NT scan cannot guarantee the health of a fetus in 100% – for a greater certainty of the result we need to always consider other important factors, such as the mother's age, blood tests and the presence of a nasal bone.

Abnormal nuchal translucency – what are the next steps?

NT scan normal range at 12 weeks shouldn't exceed 1.9 mm – during your scheduled ultrasound, the doctor found out that your baby's nuchal translucency measures 2.5 mm. What comes next?

  1. Firstly, don't panic – this measurement is not a definitive judgment. Sometimes the test may turn out wrong, even if your baby's perfectly healthy – we call this situation a false-positive result.

  2. Your doctor should schedule other tests to rule out or confirm the diagnosis – these may include more or less invasive tests:

    • NIFTY – a blood test that searches for the genetic material of a fetus present in the mother's bloodstream
    • Amniocentesis – taking a sample of the amniotic fluid
    • Cordocentesis – biopsy of an umbilical cord
    • Chorionic villus sampling – biopsy of a placenta

🤰 Don't stop here – learn about the complicated process of the pregnancy, using a variety of our tools:

Diseases connected to the abnormal nuchal fold

The nuchal translucency calculator is one of the tools that allow us to estimate the risk of various genetic diseases, which include:

Trisomies 3️⃣

The fetus has 47 chromosomes, instead of the typical 46 – one of its chromosomes is tripled.

  • Down syndrome – the fetus has one extra copy of a 21 chromosome. The severity of the disease ranges widely; heart defects and blood cancers are pretty common. The babies usually survive to adulthood.

  • Edwards syndrome – is caused by the third copy of an 18 chromosome. Babies with Edwards syndrome usually don't survive more than one year of life.

  • Patau syndrome – caused by extra genetic material accumulated in a tripled 13 chromosome. Babies affected usually die within the first year of life.

Monosomies 1️⃣

The fetus has 45 chromosomes, instead of the typical 45 – one of the chromosomes is missing.

  • Turner's syndrome – a disease that can occur only among girls – the affected baby has only one sex chromosome X, instead of two of them. The disease's course is typically light, and the children's IQ is usually within the normal range. Most of the girls born with the disease are infertile.

Percentile charts for the nuchal translucency calculator – nuchal translucency measurement chart

Our CRL and NT calculator uses the NT scan results chart presented below; all the values given in a table's body describe the thickness of a nuchal fold, given in millimeters (mm).

CRL (mm) →
Percentile ↓4550556065707580

To get the normal range of nuchal translucency at a given gestational age, you need first to convert CRL into the gestational age – you may compute it easily using our crown-rump length (CRL) calculator.

  • For example, a typical, normal nuchal translucency at 12 weeks is equal to 0.8-1.9 mm.

Of course, the nuchal translucency measurement calculator is not the only tool needed to properly assess both the pregnancy course and the growth of your baby:

How to calculate the expected nuchal translucency?

Our nuchal translucency calculator uses the following equation:

Nuchal translucency= 0.437 + (0.01969 * Crown-rump length),


  • Both Nuchal translucency and Crown-rump length are given in millimeters (mm).

Remember, it's totally alright if your child's NT is a little higher or lower than the expected value. All the NT measurements below the 95th percentile are considered normal. ✅

Nuchal translucency risk table

Take a look at the nuchal translucency measurements chart presented below; as you can see, the greater the nuchal fold thickness, the greater the risk of a genetic disorder, major abnormalities, and death.

Abnormal nuchal translucency begins at the 95th percentile – however, the risk rises significantly with much larger NT measurements. 📊

Nuchal translucencyHealthy babies bornGenetic defectFetal deathMajor fetal abnormalities
95th-99th 93%3.7%1.3%2.5%
3.5-4.4 mm70%21.1%2.7%10%
4.5-5.4 mm50%33.3%3.4%18.5%
5.5-6.4 mm30%50.5%10.1%24.2%
≥6.5 mm15%64.5%19%46.2%

❗ The nuchal translucency calculator cannot be used as a separate source of knowledge regarding any clinical or life decisions. Consult your physician for more information.

Łucja Zaborowska, MD, PhD candidate
Crown-rump length
Nuchal translucency
Estimated gestational age
Expected nuchal translucency
Your baby's in the 75th percentile.
✅ The size of nuchal translucency is within normal range.
    • Y axis: nuchal translucency in millimeters (mm).
    • X axis: gestational age in days.
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