Nuchal translucency is the fluid under the skin at the back of the baby’s neck. An increased NT is associated with chromosomal conditions such as Down syndrome and with heart defects. It is combined with blood tests and maternal age in the combined first-trimester screening test.
How to use the Nuchal Translucency Calculator
- Nuchal translucency
- Crown-rump length
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the NT and CRL from the scan report.
Inputs explained
| Field | What to enter |
|---|---|
| Nuchal translucency | In mm |
| Crown-rump length | In mm |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Valid window: CRL 45–84 mm (about 11+0 to 13+6 weeks)
NT < 3.0 mm: usually normal · 3.0–3.4 mm: borderline (above the 95th percentile for most CRLs) · ≥ 3.5 mm: increased (above the 99th percentile)
Worked example
Inputs — Nuchal translucency: 1.8 mm; Crown-rump length: 60 mm.
Results — Gestational age from CRL = 86 days; Measurement window = Within the valid window; NT result = Within the usual range.
Key terms
- NT
- Nuchal translucency.
Frequently asked questions
What is a normal NT?
Below about 3.0 mm; it increases slightly with CRL.
Does a high NT mean my baby has Down syndrome?
No – most babies with increased NT are healthy, but further tests are offered.
When is the NT scan done?
Between 11+0 and 13+6 weeks.