Nuchal Translucency Scan: When It's Done and What the Measurement Means

What is a nuchal translucency scan?

A nuchal translucency (NT) scan is a first-trimester ultrasound that measures the fluid-filled space at the back of your baby's neck, as one part of screening for Down syndrome and some other chromosomal conditions. ACOG explains that an abnormal NT measurement means an increased risk of Down syndrome (trisomy 21) or another chromosomal condition, and that it is also linked to physical differences of the heart, abdominal wall and skeleton.

The NT scan is a screening test. ACOG says screening tests tell you the chance that your baby has a condition, and that a diagnostic test such as chorionic villus sampling (CVS) or amniocentesis is needed for a more definite result. Both ACOG and the NHS say that whether you have screening is your choice.

In the US the NT scan is part of what ACOG calls first-trimester screening. In the UK it is part of the NHS combined test.

When is the nuchal translucency scan done?

The NT measurement is taken at about 11 to 14 weeks of pregnancy, because it depends on your baby's size. GeNotes, the NHS England genomics education site, says the baby's crown-rump length (head to bottom) has to be between 45 and 84 mm (about 1.8 to 3.3 inches) for the measurement. Cleveland Clinic gives 11 to 13 weeks and explains that after 14 weeks the fluid gets reabsorbed, which makes it harder to measure.

ACOG says the blood test and the NT ultrasound are usually done together between 10 and 13 weeks. In England, the NHS takes the measurement during the dating scan, which is offered at around 10 to 14 weeks and usually takes about 20 minutes. The NHS says you may need a full bladder for it, so ask beforehand.

The NHS does not offer the combined test if your dating scan is after 14 weeks. You will be offered the quadruple blood test between 14 and 20 weeks instead, which screens for Down's syndrome only and is not as accurate as the combined test.

What does the nuchal translucency measurement mean?

A small amount of fluid at the back of the neck is normal, and a larger measurement raises the chance of a chromosomal, genetic or heart condition without diagnosing one. GeNotes says up to 3.5 mm of fluid is normal and that any pregnancy with an NT above 3.5 mm should be offered genetic testing. Cleveland Clinic says that if the measurement is higher than 3 mm at 12 weeks, your provider will usually talk with you about more testing.

GeNotes says extra fluid is also seen in healthy babies, and that the chance of an underlying condition rises with the measurement. In its figures, about 70% of babies with an NT of 3.5 to 4.4 mm are alive and well. After an abnormal result, Cleveland Clinic says, your provider may also suggest a fetal echocardiogram, a closer look at the baby's heart.

GeNotes says the measurement is rarely used on its own. Cleveland Clinic says providers usually combine all the first-trimester results and give the answer as a chance, for example 1 in 300.

What is the combined test?

The combined test is the NHS first screening test for Down's, Edwards' and Patau's syndromes, and it puts together the NT measurement, a blood test and your age. The NHS offers the blood test between 10 and 14 weeks and the neck measurement at the 12-week scan, usually at the same appointment. ACOG's version, first-trimester screening, pairs the NT scan with a blood test that measures two substances.

GOV.UK, which publishes the NHS screening leaflets, says any result up to 1 chance in 150, such as 1 in 100, counts as higher chance, and 1 in 151 or more, such as 1 in 300, counts as lower chance. Around 3 out of every 100 results are higher chance. The NHS says results come within 2 weeks, and that if the chance is higher, someone will contact you by phone or in person within 1 week.

The NHS says most people with a higher-chance result have a baby without any of the conditions. You can choose to be screened for all three conditions, for Down's syndrome only, for Edwards' and Patau's only, or for none. The NHS usually explains these options at your booking appointment, the UK name for your first prenatal appointment.

How accurate is the nuchal translucency scan?

The NT measurement alone finds most babies with Down syndrome, and Cleveland Clinic and GeNotes both say that combining it with other first-trimester tests makes screening more accurate. Cleveland Clinic says NT alone detects about 70% of Down syndrome cases. GeNotes puts it at around 80% for Down syndrome and other major chromosomal conditions, at a false-positive rate of 5%.

Cell-free DNA screening, often called NIPT, is more accurate for the three common trisomies. ACOG's January 2026 practice advisory, which endorses guidance from the Society for Maternal-Fetal Medicine, calls cell-free DNA the most sensitive and specific screening test for trisomies 21, 18 and 13 and recommends that it be routinely available to all patients. The advisory also says the first-trimester ultrasound can find things cell-free DNA may not, including structural differences in the baby. On the NHS, NIPT is offered as a second test after a higher-chance combined result.

What happens after a higher-chance result?

After a higher-chance result, the NHS says you can choose NIPT, a diagnostic test, or no further tests. ACOG says your obstetrician or a genetic counselor will explain what the result means and help you decide on the next steps.

GOV.UK describes the two diagnostic tests. CVS takes a small sample from the placenta and is usually done from 11 to 14 weeks. Amniocentesis takes a small sample of the fluid around the baby and is usually done after 15 weeks. GOV.UK says about 1 in 200 people (0.5%) who have a diagnostic test will miscarry because of it.

You will still be offered the 20-week anatomy scan, whatever your first-trimester result. ACOG's 2026 advisory recommends an anatomy survey for all patients regardless of the screening method, and GOV.UK says the NHS offers the 20-week scan to screen for Edwards' and Patau's syndromes as well.

When should you call your doctor or midwife?

• You are 10 to 14 weeks pregnant and have not been offered screening. The NHS asks you to tell your midwife or GP.
• You have not had your combined test results within 2 weeks. The NHS asks you to contact your midwife, health visitor or GP.
• You are unsure which test suits you. ACOG says your health care professional can tell you the false-positive and false-negative rates of each test.
• You had a higher-chance result. The NHS offers an appointment with a health professional to go through the result and your choices before you decide on more tests.