GUIDE
The NT scan measures the fluid-filled space at the back of your baby's neck between weeks 11 and 14 to assess the risk of Down syndrome and other conditions.
A normal NT measurement is typically less than 3.0 mm. The NT scan is a screening tool — it does not diagnose conditions but helps determine whether further testing is recommended. It is often combined with a blood test for more accurate risk assessment.
Be prepared from day one
The nuchal translucency (NT) scan is a specialized ultrasound performed between 11 weeks and 13 weeks 6 days of pregnancy. It measures the translucent (fluid-filled) space at the back of the baby's neck. All babies have some fluid here — the measurement itself is what matters.
The NT scan is part of first-trimester screening and is typically offered alongside (or as an alternative to) the NIPT blood test. While NIPT has a higher detection rate for chromosomal conditions, the NT scan provides additional information — particularly about potential heart defects — that NIPT cannot assess.
This scan must be performed by a trained and certified sonographer. The timing window is strict: it can only be done when the baby's crown-rump length is between 45 and 84 mm, which corresponds to about 11 to 14 weeks.
The NT scan is a screening tool that assesses risk — it does not provide a definitive diagnosis for any condition.
The NT scan is most informative when combined with a first-trimester blood test (drawn at weeks 10-13) that measures two markers: free beta-hCG and PAPP-A. Together, these results plus your age produce a combined risk score.
Combined first-trimester screening detects about 82 to 87 percent of Down syndrome cases when using a 1-in-300 risk cutoff, with a false positive rate of about 5 percent. The NIPT has a higher detection rate (above 99 percent for Down syndrome), which is why many people now choose NIPT as their primary screening method.
Your provider will help you decide which screening approach makes the most sense for you. Some people choose both NT and NIPT for the most comprehensive information.
| Component | Type | What It Tells You |
|---|---|---|
| NT measurement | Ultrasound | Fluid at back of baby's neck — thicker measurement = higher risk |
| Free beta-hCG | Blood test | Higher levels associated with increased risk of Down syndrome |
| PAPP-A | Blood test | Lower levels associated with increased risk of chromosomal conditions and placental issues |
| Maternal age | Clinical factor | Risk of chromosomal conditions increases with maternal age |
The NT measurement must be very precise. The sonographer needs exact positioning to get an accurate result.
An NT measurement below 3.0 mm is generally reassuring. The average NT at 12 weeks is about 1.3 mm, and the measurement naturally increases slightly as the baby grows — which is why it must be interpreted relative to crown-rump length.
An NT measurement of 3.0 mm or above is considered increased and raises the statistical risk of chromosomal conditions and certain structural anomalies, particularly heart defects. However, many babies with a mildly increased NT (3.0 to 3.5 mm) are born perfectly healthy.
An NT measurement above 3.5 mm carries a higher statistical risk and will prompt your provider to recommend further evaluation — typically NIPT (if not already done), a detailed early anatomy scan, a fetal echocardiogram, and possibly amniocentesis or CVS for definitive chromosomal analysis.
The NT scan tells you about risk — not certainty. An increased measurement means more information is needed, not that something is wrong. If your result is elevated, a genetic counselor can help you understand the numbers and navigate your options for further testing.
If your NT measurement and combined screening results are low risk, no further chromosomal testing is typically needed. You will continue with your regular prenatal care schedule, with the anatomy scan as the next major ultrasound.
If the results indicate elevated risk, your provider will discuss next steps. Options include NIPT for additional non-invasive screening, CVS (chorionic villus sampling) for definitive results between weeks 10 and 13, or amniocentesis for definitive results after week 15. A genetic counselor can walk you through the pros, cons, and accuracy of each option.
For the full picture of first-trimester testing, see our pregnancy blood tests guide and our guide on the dating ultrasound.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
