Nuchal Translucency Calculator

Enter your baby's Crown-Rump Length (CRL) and the measured Nuchal Translucency (NT) thickness from your ultrasound scan to get the NT percentile, expected NT value, and an indication of whether the measurement falls within the normal range. The Nuchal Translucency Calculator helps you understand your first-trimester screening results by comparing your NT measurement against gestational norms.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

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CRL is measured during your first-trimester ultrasound, typically between 11–14 weeks.

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The NT thickness is measured as part of the first-trimester combined screening test.

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Results

NT Percentile

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Expected NT for CRL

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NT / Expected NT Ratio

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Estimated Gestational Age

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NT Assessment

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Frequently Asked Questions

What is the nuchal translucency test?

The nuchal translucency (NT) test is an ultrasound screening performed between 11 and 14 weeks of pregnancy. It measures the fluid-filled space at the back of the baby's neck. A thicker NT measurement can indicate a higher risk of chromosomal conditions such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), or Patau syndrome (trisomy 13). The NT result is typically combined with blood tests (PAPP-A and hCG) for a more accurate risk assessment.

How is the expected nuchal translucency calculated?

The expected NT value is calculated based on the baby's Crown-Rump Length (CRL) using the formula: Expected NT = 0.437 + (0.01969 × CRL in mm). This formula, derived from large population studies, provides a baseline against which your measured NT can be compared. Your measured NT is then expressed as a multiple of the median (MoM) or a percentile rank.

What is a normal NT scan result at 12 weeks?

At 12 weeks (CRL approximately 60 mm), the expected NT is around 1.6 mm. An NT measurement below the 95th percentile is generally considered within the normal range. Most guidelines use an NT of less than 3.0 mm as the upper limit of normal, though risk assessment considers the NT in conjunction with CRL and maternal blood markers for a fuller picture.

Is an NT measurement of 0.8 mm at 12 weeks considered normal?

Yes, an NT of 0.8 mm at 12 weeks is well within the normal range. The expected NT at this gestational age is approximately 1.6 mm, so 0.8 mm would fall below the median — which is not a cause for concern. Very low NT values are not associated with increased genetic risk.

What NT measurement is considered high or abnormal?

An NT measurement at or above 3.0 mm, or above the 99th percentile for the CRL, is generally considered elevated and warrants further investigation. Higher NT values are associated with increased risks of chromosomal abnormalities, cardiac defects, and other structural issues. However, many babies with a high NT measurement are born healthy — the result is a risk indicator, not a diagnosis.

What disorders are associated with an abnormal nuchal fold thickness?

An abnormally thick NT is associated with chromosomal conditions including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), and Turner syndrome (45,X). It can also be linked to congenital heart defects, skeletal dysplasias, and other structural abnormalities. The risk rises progressively with NT thickness above the 95th percentile.

Can a normal nuchal translucency scan guarantee my baby is healthy?

No, a normal NT scan cannot guarantee the health of the fetus. It significantly reduces the probability of certain chromosomal conditions but is a screening test, not a diagnostic one. Some chromosomal and structural conditions may not affect NT thickness. For a more definitive answer, diagnostic tests such as chorionic villus sampling (CVS) or amniocentesis can be offered to high-risk pregnancies.

How does gestational age relate to the NT measurement?

NT naturally increases with gestational age, which is why it must always be interpreted in relation to the CRL (a proxy for gestational age). The NT scan window is 11 to 14 weeks (CRL 45–84 mm). Outside this window, the measurement is less reliable. This calculator uses the CRL to estimate gestational age and calculate the expected NT value for comparison.