Nuchal Translucency Calculator

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Measured from the top of the head to the bottom of the spine. Valid range for NT screening: 45-84 mm (11+0 to 13+6 weeks).
mm
The fluid-filled space at the back of the fetal neck, measured on ultrasound. Normal values are typically below the 95th percentile for the given CRL.
mm
Used to calculate the background risk of trisomy 21 before combining with the NT measurement.
years
NT percentileNormal range
64.5%

Percentage of unaffected pregnancies at this CRL with a lower NT measurement

Expected (median) NT1.62mm
NT MoM1.11
Gestational age12w 3d
Adjusted trisomy 21 risk1 in 1,657
NT categoryLow risk
64.5 %
Below median<50Normal range50-95Borderline elevated95-99Elevated99+

NT is low risk at the 64.5th percentile.

  • NT of 1.8 mm at CRL 60 mm places this measurement at the below the 95th percentile (64.5th).
  • The MoM of 1.11 means the measured NT is 11% above the expected median for this gestational age.
  • Adjusted trisomy 21 risk combining maternal age (30 years) with NT: 1 in 1,657.
  • NT screening alone detects approximately 75% of trisomy 21 cases; combined first-trimester screening (NT + PAPP-A + free beta-hCG) raises detection to about 90%.

Next stepA measurement below the 95th percentile is reassuring. Discuss combined first-trimester screening (NT plus blood tests) with your provider for a more comprehensive risk estimate.

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