It is one of the basic pillars of prenatal screening in the first trimester
It is done at end of first trimesterand serves to evaluate the risk of the baby developing Down syndrome or other chromosomal abnormalities.
What is nuchal translucency?
The nuchal translucency is a collection of fluid under the skin at the back of the neck of the fetus.
All babies have a little fluid in the nape area, but in babies with Down syndrome the amount of fluid is greater, and therefore the measurements are larger.
When is the nuchal fold measured?
Nuchal translucency exploration should be done at a certain point in pregnancy, approximately between week 11 and week 14 of pregnancy.
This test should not be done prematurely because the baby is still very small, nor after week 14, since the excess nuchal fluid can be absorbed by the lymphatic system of the fetus, and therefore the test would not be accurate.
|Left image NT. nuchal fold increased. Right image NT normal nuchal fold|
How is the nuchal translucency test done?
The examination is usually performed using a ultrasound in the abdomen.
It is usually advisable to go to the examination for the nuchal examination with a full bladder, since this way the bladder pushes the uterus and allows a clearer vision to be obtained. It is a painless test, although some pressure may be felt in the abdomen. Nuchal fold measurement can detect about 77% of babies with Down syndrome. The nuchal translucency test can only estimate risk that your baby has Down syndrome. Not 100% reliable. The risk is expressed as a percentage, so if the result is 1 in 1000, it means that out of every 1,000 babies with that level of risk, 1 will have Down syndrome. A risk of 1 in 150 or less is considered a high risk. In this test false positives may occur when the results may suggest that a baby is at high risk for Down syndrome, even though the risk is really low. The false positive rate for this type of test is 5%. That is why the measurement of the nuchal fold is combined, together with the results of a blood test, in which the levels of the hCG beta hormone and of the PAPP-A protein. In babies with Down syndrome, levels of the hormone hCG beta are high and the protein PAPP-A is low. To assess risk, other factors such as the mother's age are also taken into account. When the nuchal fold measurement is combined with the results of the blood test, the detection rate increases to 90%. The false positive rate for the combined test is also 5%.
What if the risk is high?
If the results of the nuchal translucency indicate that there is little possibility that the fetus has Down syndrome, it is most likely that no further testing is necessary. Is the measurement of the nuchal fold reliable?
If the fold is thicker than normal, it is considered that there is a high risk of having a baby with Down syndrome, and the need to undergo a amniocentesis or a chorionic villus analysis for a more reliable diagnosis.
Both amniocentesis and chorionic villus analysis are the only tests that can tell for sure if a baby has Down syndrome, but both have a small risk of miscarriage.