Nuchal Fold Testing for Down Syndrome

Nuchal Translucency Screening

Pregnant Woman Having An Ultrasound at doctor's office, female gynecologist, selective focus to transducer
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Why the test is done:

To screen for Down Syndrome, heart abnormalities as well as other anomalies. This test or a similar test should be offered to every mother in prenatal care, this is not just for mothers who are over age 35, though they have an increased risk of a baby born with Down Syndrome or other genetic problems. Remember, a screening is not a diagnosis, but a positive screen means that there is a higher likelihood that your baby is affected.

 

How the test is done:

An ultrasound is done between weeks 11-14 to measure the translucent area in the skin on the back of your baby’s neck, known as the nuchal fold. This feels like a regular ultrasound for the mother.

When the test is done:

Usually between 11-14 weeks gestation (from LMP). Doing it outside of this range makes the test not accurate. There are studies being done to set the reference ranges for the nuchal fold thickness at other gestation ages.

How the results are given:

Usually as positive or negative, with about a 5% false positive rate. A positive screen indicates that there is a higher than normal chance that your baby has Down Syndrome. Everyone has a risk of having a baby with Down Syndrome, so a negative screen is not the same thing as a clean bill of health. This can be surprising when a mother has a negative screen but a baby who has Down Syndrome is born.

Risks involved:

There is no risk to the test itself.

Though it may be difficult to understand the results. This is a screening exam, used to help you understand your risk of genetic complications with your pregnancy. So you come into your pregnancy with a certain amount of risk of Down Syndrome. This screening test can alter the risk assessment. For example at 35 I have a 1 in 270 risk of having a baby with Down Syndrome.

If my nuchal fold screening shows an average size fold, the risk is the same. If the fold is thinner my risk drops, but if it is thicker my risk may increase. This is where the recommendation for further genetic testing may come in.

Alternatives:

If the test is positive or if you are simply needing to know definitively, there are alternative tests available. You can use more invasive testing like amniocentesis or chorionic villus sampling (CVS), but these run added risks to the pregnancy, though are more accurate and are a diagnostic test rather than a screening. Some of these can be done earlier in pregnancy that the nuchal fold testing.

Where do you go from here?

If the nuchal fold translucency screening is positive, you may be advised to go for more invasive testing like amniocentesis or chorionic villus sampling (CVS). This is completely up to you. There are also more intensive ultrasound that can be done later that are also considered screenings, but are less invasive and don't carry the risks that invasive testing carries.

Other Resources:

Sources:

Chasen ST, Sharma G, Kalish RB, Chervenak FA. First-trimester screening for aneuploidy with fetal nuchal translucency in a United States population. Ultrasound Obstet Gynecol. 2003 Aug;22(2):149-51.

Sheppard C, Platt LD. Nuchal translucency and first trimester risk assessment: a systematic review. Ultrasound Q. 2007 Jun;23(2):107-16.

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