Nuchal translucency: what this test is and how it works for fetal chromosomal abnormalities
Nuchal translucency is a screening test used to detect the risk of chromosomal abnormalities in the fetus during pregnancy. This examination, different from an "ultrasound, allows to identify the risk that the fetuses may be affected by Down syndrome and more.
Warning: this examination highlights a risk for fetuses of having Down syndrome: it does not give absolute certainty, but only the possibility. they identify about 75/80, while the false positives are about 5-8% (the fetuses, that is, which are positive, but which are not). After this test, it is possible to proceed with other tests such as the chromosomal one on fetal cells after CVS or amniocentesis, in order to obtain a proper prenatal diagnosis.
Let's try to understand when it is good to perform this test during pregnancy, how it works and why combine it with the duotest in the so-called "combined test". But first, here's a great video to raise awareness against prejudices for Down syndrome:
Nuchal translucency: when to perform the exam and how to interpret the results
The test must be performed between the eleventh and fourteenth week of pregnancy and is carried out using ultrasound, ie sound waves that our ear cannot perceive and which are absolutely not harmful to the fetus or the future mother.
Ultrasounds allow the reactions of tissues set in vibration to be detected during the test, which then return to the computer in the form of an electrical signal, capable of processing them into images. The fetal neck has an area that does not reflect these ultrasounds, which is why it is called "translucent". A liquid is concentrated in this area of the fetal nape and appears around the tenth week of pregnancy, only to be eliminated after the fourteenth. That is why, in order to obtain a possible prenatal diagnosis, it is necessary to do the examination no later than that period.
A fetus with Down Syndrome (the risk of which increases with increasing maternal age) shows excessive thickness in the nuchal translucency zone: the thicker that zone, the higher the risk. We repeat, however, that it is only a question of risk: the thickness can also be determined by different pathologies such as heart problems or anemia or more. In fact, in the case of nuchal translucency, we speak only of screening tests.
Further tests will therefore be necessary to ascertain the result, such as the chromosomal examination on fetal cells after CVS or amniocentesis. Since these tests may involve a risk of miscarriage (however small) it is always good to perform them only after nuchal translucency. , which is safe for the fetus and pregnant woman.
How does this screening test work and how long does it last?
The nuchal translucency test can have a variable duration, as different measurements are required for different fetal positions. However, the exam is unlikely to exceed 45 minutes in duration. The translucency is always performed by expert operators and can take place transabdominally or transvaginally: the second case can cause greater discomfort, but generally allows images to be obtained with a better resolution.
To make the test more complicated there may be several factors such as the obesity of the mother or the presence of fibroids in the uterine wall.
Nuchal translucency and duotest: what is the combined test
The combined test is nothing more than the combination of nuchal translucency with another test, the so-called "duotest", useful for increasing the reliability of the result of the first in detecting chromosomal abnormalities and Down syndrome.
The duotest consists of the simultaneous blood test of chorionic gonadotropin and PAPP-A (plasma protein A associated with pregnancy). The risk of Down Syndrome is greater if an increase in gonadrotropin and a decrease in PAPP-A are found in the venous blood of the expectant mother.
Maternal age is undoubtedly a risk factor which is taken into account in detecting the blood concentration of these two substances. The duotest thus allows to obtain a more certain result: thus up to 90% of cases of Down Syndrome are identified ( only 5% are false positives.) However, since the diagnosis is not yet fully carried out, it will be better to proceed with more invasive tests such as CVS or amniocentesis.
For more scientific information, you can visit the website of the International Evangelical Hospital.
