# Nuchal Translucency Calculator

URL: https://speedycalculator.com/calculators/health/nuchal-translucency/
Last updated: 2026-10-30

> The nuchal translucency calculator checks whether a first-trimester NT measurement is within the expected range for the crown-rump length, and flags increased NT that warrants further screening.

## Inputs

- Nuchal translucency (mm)
- Crown-rump length (mm)

## Results

- Gestational age from CRL
- Measurement window
- NT result

## 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)
```

## Explanation

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

FieldWhat to enterNuchal translucencyIn mmCrown-rump lengthIn 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.*

## 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.

## FAQ

**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.


## Sources

- [Fetal Medicine Foundation – Nuchal translucency](https://fetalmedicine.org/education/the-11-13-weeks-scan)