Use the crown-rump length from your ultrasound report to see NT reference values for that measurement.
Your NT reference results
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These are reference-distribution estimates, not a diagnosis or a prediction of an individual screening result.
Methodology
This page estimates reference NT values from the entered CRL. It does not interpret an individual NT measurement.
The calculator estimates gestational age from CRL with the Robinson-Fleming dating equation. NT reference values and approximate percentiles use the unaffected-pregnancy distribution described by Wright and colleagues. These are reference estimates, not a diagnosis or a personal chromosome-condition chance.
NT screening is normally interpreted with the full ultrasound and, where relevant, other screening information. The CRL and NT should be from the same scan. If your report gives NT and gestational age but not CRL, ask your ultrasound service for the CRL rather than converting weeks and days into a precise percentile.
Sources
- Wright et al., NT reference distribution
- Perinatal Institute, CRL dating policy
- NHS FASP screening handbook
If your result needs follow-up
An NT result is one part of screening and cannot calculate an individual chance by itself. Follow the plan from your ultrasound service or clinician. If your report says the NT is 3.5 mm or more, contact the service that arranged the scan if you have not already been given follow-up advice.