Nuchal Translucency Screening

Learn more about NT screening, an early, noninvasive option that can be exciting news for parents concerned about genetic disorders.
Prenatal Testing

A nuchal translucency screening, or NT screening, is a routine ultrasound performed between week 11 to week 14. Fetuses with increased fluid at the base of their necks — a spot known as the nuchal fold — may have an extra chromosome. This fluid can be measured with ultrasound when the base of the neck is still transparent. Because the nuchal fold becomes less transparent as your baby grows, timing is crucial. In addition to Down syndrome, NT screens for congenital heart defects and other genetic disorders.

Nuchal translucency is a screening, which means the results are can't tell you for sure whether your child has a chromosomal disorder. That's why it's often combined with other data (including blood test like noninvasive prenatal tests (NIPT) and population studies) to provide a statistic about the likelihood of such a disorder.

Who nuchal translucency screening is for

NT screening is available for any pregnant woman. Though it can't give you the definitive diagnosis you'd get from more invasive diagnostic tests, it can help you decide whether you want to undergo diagnostic testing.

How nuchal translucency screening is done

This procedure is a special type of ultrasound. A sonographer will first move the transducer across your belly to measure your baby from crown to rump to ensure that the fetal age is accurate. Then he or she will locate and measure the nuchal fold (if you're lucky your baby will cooperate by moving into a position where the measurement will be easy).

If your screening test shows that your baby may be at an increased risk for having a chromosomal defect, a diagnostic test like chorionic villus sampling (CVS) or amniocentesis will be offered.

When nuchal translucency screening is done

Since NT screening must be done between weeks 11 and 14, an accurate date of conception is important for an accurate result.

First-trimester combined screening

NT screening can be combined with blood tests, known as the first trimester combined screening, for more definitive results. A first trimester blood test measures hCG and a pregnancy protein called PAPP-A (pregnancy associated plasma protein A), two hormones produced by the fetus and passed into the mother's bloodstream. Low levels of PAPP-A early in pregnancy indicate increased risk of genetic abnormalities, heart problems and preterm birth. These levels, combined with the results of NT screening and the mother's age, can provide a risk assessment for Down syndrome and trisomy 18.

The results of an NT screen can also be combined with a second trimester blood test called the quad screen, which provides a risk assessment using four entirely different markers present in the maternal bloodstream (this is known as the fully integrated screen). Or you may be given the results of the first trimester screen and the quad screen separately (known as stepwise sequential screening). Or your practitioner may combine the results of the NT screen with the results of NIPT to provide you with a risk assessment.

How accurate is it?

The nuchal translucency and the associated blood work don't directly test for chromosomal problems, nor do they diagnose a specific condition. Rather, the results merely provide you with your baby's statistical likelihood of having a problem. An abnormal result on the nuchal translucency or combined screening test doesn't mean that your baby has a chromosomal problem, just that he or she has an increased risk of having one. In fact, most women who have an abnormal result on their screening test go on to have a perfectly normal and healthy child. At the same time, a normal result is not a guarantee that your baby is normal, but it does mean that it's very unlikely your baby a chromosomal defect.

The accuracy of the test is dependent on the skill of the sonographer performing it and the sensitivity of the equipment. The American College of Gynecologists and Obstetricians recommends that NT screening be performed only at specialized centers; talk to your practitioner or do some research to see what's available in your area.

The first-trimester combined screening can detect approximately 80 percent of Down syndrome and 80 percent of trisomy 18 problems.


Both the ultrasound and the accompanying blood tests are painless (unless you count the needle prick for the blood test) and carry no risk for you or your baby. The biggest problem might be the anxiety they can provoke. False positives are common (as are false negatives), which may lead to follow-up procedures that present greater risk. But try to keep it in perspective: The odds of having a completely healthy baby are overwhelmingly in your favor. The NT screen is best thought of as a decision-making tool. Before you decide whether to have this procedure, talk to your practitioner about genetic counseling to help you determine which genetic tests are right for you.

Updated 2/11/15