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Nuchal Translucency (NT) Calculator

Calculate your risk assessment for chromosomal abnormalities based on NT measurement, maternal age, and blood markers.

Maternal Information

Lowest Risk: 18-25 Higher Risk: 35+
NT Scan Window: 11-14 weeks

NT Measurement

Normal: ≤ 2.5mm Increased: > 2.5mm
11 weeks: 45-54mm 14 weeks: 80-84mm

Blood Markers (Optional)

Normal: ≥ 0.5 MoM Low: < 0.5 MoM
Normal: 0.5-2.0 MoM High: > 2.0 MoM

Risk Assessment Results

Estimated Risk for Down Syndrome

1 in 850
Low Risk

This is considered a low-risk result. Your chance is similar to the general population risk for your age.

Down Syndrome Risk

1 in 850

Population risk: 1 in 1,000

Edward Syndrome Risk

1 in 5,000

Trisomy 18 risk

Patau Syndrome Risk

1 in 8,000

Trisomy 13 risk

Detection Rate

85-90%

With combined screening

Recommendations

Based on your low-risk result, no further invasive testing is typically recommended. Continue with routine prenatal care.

Next Steps: Routine anomaly scan at 18-20 weeks.

What is Nuchal Translucency?

Nuchal translucency (NT) is a sonographic feature representing the normal subcutaneous fluid-filled space between the back of the fetal neck and the overlying skin.

Why Measure NT?

The NT measurement, when combined with maternal age and blood markers, helps assess the risk of:

  • Down syndrome (Trisomy 21) - Most common chromosomal abnormality
  • Edward syndrome (Trisomy 18) - More severe chromosomal disorder
  • Patau syndrome (Trisomy 13) - Rare chromosomal disorder
  • Cardiac defects - Some heart abnormalities

Normal NT Measurements

11 weeks: Normal range: 1.0-2.0 mm

12 weeks: Normal range: 1.0-2.5 mm

13 weeks: Normal range: 1.0-2.8 mm

14 weeks: Normal range: 1.0-3.0 mm

The NT Screening Procedure

The NT scan is typically performed between 11 and 14 weeks of pregnancy.

Step-by-Step Process:

  • Timing: Best performed at 12-13 weeks gestation
  • Ultrasound: Transabdominal ultrasound is usually sufficient
  • Measurement: NT is measured in millimeters (mm)
  • CRL: Crown-rump length is measured for accurate dating
  • Blood Test: PAPP-A and free β-hCG may be tested (combined screening)

What to Expect:

  • Procedure takes 20-30 minutes
  • No special preparation needed
  • Results usually available immediately
  • Non-invasive and safe for mother and baby

Interpreting Your Results

Risk Categories:

Low Risk

Risk less than 1 in 250. No further testing typically recommended.

Intermediate Risk

Risk between 1 in 250 and 1 in 1000. Consider non-invasive prenatal testing (NIPT).

High Risk

Risk greater than 1 in 250. Discuss diagnostic testing options with your doctor.

Understanding the Numbers:

  • 1 in 850 means 1 chance in 850 pregnancies
  • This equals approximately 0.12% chance
  • For comparison, the general population risk for a 30-year-old is about 1 in 1000

Important Limitations

What NT Screening CAN Do:

  • Provide a risk assessment, not a diagnosis
  • Detect 85-90% of Down syndrome cases (with combined screening)
  • Identify increased NT which may indicate other problems
  • Help determine need for further testing

What NT Screening CANNOT Do:

  • Provide a definitive diagnosis of chromosomal abnormalities
  • Detect all birth defects or genetic conditions
  • Guarantee a healthy baby
  • Replace diagnostic testing like amniocentesis or CVS

Important Disclaimer

This calculator provides an estimate based on statistical models. It is NOT a medical diagnosis. Always consult with your healthcare provider for professional medical advice and interpretation of your screening results.

The results should be discussed with a genetic counselor or obstetrician who can consider your complete medical history and provide personalized recommendations.