Nuchal Translucency Calculator
Assess chromosomal abnormality risk from first trimester ultrasound measurements
Calculate Nuchal Translucency Risk
Fetal length from crown to rump (typically 35-100mm at 11-14 weeks)
Thickness of fluid-filled space at back of fetal neck
Leave empty to auto-calculate from CRL (11-14 weeks = 77-98 days)
Example Calculation
Normal NT at 12 Weeks
Crown-rump length: 60mm
Measured NT: 1.5mm
Expected NT: 0.437 + (0.01969 × 60) = 1.62mm
Gestational age: ~12 weeks 2 days
Result
Percentile: 50th-75th percentile
Risk assessment: Normal range (<95th percentile)
Recommendation: Continue routine prenatal care
NT Risk Categories
Normal Range
<95th percentile
97% normal babies, 0.2% chromosomal abnormalities
Increased Risk
95th-99th percentile
93% normal babies, 3.7% chromosomal abnormalities
Elevated Risk
3.5-4.4mm
70% normal babies, 21% chromosomal abnormalities
Very High Risk
≥6.5mm
15% normal babies, 64.5% chromosomal abnormalities
NT Reference Guide
Conditions Detected:
- • Down syndrome (Trisomy 21)
- • Edwards syndrome (Trisomy 18)
- • Patau syndrome (Trisomy 13)
- • Turner syndrome
- • Cardiac defects
Understanding Nuchal Translucency Screening
What is Nuchal Translucency?
Nuchal translucency (NT) is the measurement of the clear space in the tissue at the back of a developing baby's neck during the first trimester (11-14 weeks). This ultrasound measurement helps assess the risk of chromosomal abnormalities and certain genetic conditions.
Why is NT Screening Important?
- •Early detection of chromosomal abnormalities (Down syndrome, Edwards syndrome)
- •Assessment of cardiac defects and other structural abnormalities
- •Risk stratification for further diagnostic testing
- •Combined screening with maternal blood tests
NT Calculation Formula
Expected NT = 0.437 + (0.01969 × CRL)
- NT: Nuchal Translucency (mm)
- CRL: Crown-Rump Length (mm)
- Percentile: Comparison to population norms
Follow-up Testing
Important: NT screening is not diagnostic. Abnormal results require additional testing and genetic counseling for definitive diagnosis.