The nuchal translucency scan is usually the first detailed look at your baby. It is done between 11 weeks and 13 weeks 6 days of pregnancy, when the baby measures roughly 45 to 84 mm from head to bottom. Outside that window the measurement cannot be used, so it is worth booking as soon as your dating scan gives you a due date.
What the scan measures
Every baby has a small pocket of fluid under the skin at the back of the neck. That space - the nuchal translucency - is measured to a tenth of a millimetre. A thicker measurement is linked to a higher chance of chromosomal conditions such as Down syndrome, and of some heart conditions.
The same scan is also used to:
- confirm the baby’s heartbeat and the due date
- count the babies and, for twins, check whether they share a placenta
- look for major structural problems that are already visible at this stage
- check blood flow in the uterine arteries, which helps estimate the risk of pre-eclampsia
Combined screening: scan plus blood test
The NT measurement is combined with your age and a blood test (free beta-hCG and PAPP-A) to calculate a chance for the three common trisomies. The result is a figure such as 1 in 5,000 or 1 in 50, not a yes-or-no answer. Accreditation from the Fetal Medicine Foundation (UK) means the measurement is taken to an audited standard, which keeps that calculation reliable.
If the result is higher chance
A higher-chance result means more information would help - it does not mean the baby has a condition. Most babies with a higher-chance result are healthy. The next steps are discussed at a counselling visit and may include:
- cell-free DNA screening (NIPT) from a blood sample
- chorionic villus sampling (CVS) now, or amniocentesis from 15 weeks, for a diagnostic answer
- an early fetal echocardiogram and a careful anomaly scan at 18–22 weeks
How to prepare
- Bring your dating scan report so the right week is confirmed
- Most NT scans are done through the abdomen; a moderately full bladder can help
- The scan takes 20–40 minutes; the baby sometimes needs to move into position
- Your partner or a family member is welcome in the room
Pre-natal sex determination is prohibited under the PCPNDT Act. The sex of the baby is not detected or disclosed at any scan.
Related care: Fetal medicine and pregnancy scans
More patient guides
- High blood pressure in pregnancy: the warning signs you should not wait on
- Expecting twins? Why “do they share a placenta?” is the first question
- NIPT or NT scan: which test do you need, and can one replace the other?
- Pregnancy after 35: fertility, risks and how to plan a healthy pregnancy
- Uterine fibroids: symptoms, when to treat, and the options available
This guide is general information for patients and does not replace a consultation with your own doctor.