Nuchal translucency: what it is, when and why to do it

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Marie-Ange Demory
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Translucenza nucale

What it is and how it takes place

La translucenza nucale (comes acronym NT, i.e. Nuchal Translucency) is a exam which consists of aexternal ultrasound, harmless for the unborn child, with which the thickness of a collection of liquid located under the fetal neck is measured, that is, in practice, the distance between the skin of the nape and the occipital bone of the skull. “It is the most important fetal marker for predicting a series of fetal abnormalitiesHe explains Paolo Cavoretto, obstetrician gynecologist, expert in prenatal diagnosis of the obstetrics and gynecology department of theSan Raffaele hospital in our city. It means that if its value is altered compared to the norm, the presence of a fetal anomaly can be suspected, which will however be confirmed with a more precise diagnostic system.

How long does it last? Is it painful?

Sometimes the exam can last longer than 30-45 minutes, due to the need to take multiple measurements with the fetus in well-established positions.

It can be glitzy but not painful.

Is it an internal or external ultrasound?

Nuclear translucency is an external ultrasound.

Is nuchal translucency mandatory?

No, the translucency nucale non it is mandatory although strongly recommended.

In this article

  • When performing nuchal translucency 
  • Nuclear translucency: values 
  • Where to do the nuchal translucency 
  • Nuchal translucency: cost
  • Nuclear translucency and bitest
  • The result of the bitest

Pictures of the fetus from 4 to 40 weeks

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When performing nuchal translucency

This measurement can theoretically be performed at any time in the pregnancy, "But it is in particular fromeleventh to fourteenth week of gestation which allows to estimate more accurately the risk that the fetus is affected by chromosomal pathologies such as trisomy 21 (down syndrome), trisomies 18 or 13, Turner Syndrome, or other congenital anomalies, especially cardiac malformations ".

Read also: How prenatal diagnosis works

Nuclear translucency: values

"In order to carry out this examination - explains Cavoretto - the cranial-caudal length of the fetus (CRL) must be between 45 millimeters and 84 millimeters". Since the value of the nuchal translucency varies according to this length, it is impossible to give threshold values ​​for normality: the outcome of the examination must be evaluated on the basis of particular curves that take this ratio into account.

How to read the exam results

«Generally, we speak of increased translucency, that is that it could be an indication of problems, above 3,5mm. But also values lower could be at risk, because in any case linked to the length of the fetus ».

Where to do the nuchal translucency

To carry out this examination it is good to contact specialized centers. «The advice is to choose centers that adhere to the guidelines of scientific societies such as The Fetal Medicine Foundation, the foundation of the inventor of this practice. Periodically, the operators who adhere to this foundation send their results to supervisors, who check their performance: there is therefore an annual audit and control process. And if certain quality requirements are not respected, the license is also suspended, i.e. the software that allows you to do the calculations to estimate the translucenza nucale».

The website of the Del Paesena Society of Obstetric and Gynecological Ultrasound and Biophysical Methodologies ( provides the list of certified centers. “In addition, you can directly contact the center where you want to take the test and ask if it is carried out according to the requirements of the Fetal Medicine Foundation.

Nuchal translucency: cost

L'obstetric ultrasound with nuchal translucency, in conjunction with the measurement of placental markers in maternal blood (bitest), has been included in the new essential levels of care, such as examination for pregnancy passed by National Health Service to all women. So soon it should be free in all regions, even if some will probably take a while to implement these indications.

When it is not completely free of tickets, the cost of the bitest in the public sphere is around 60 €. "In the private health system, the costs are around from 200 to 300 euro for translucency with bitest », informs the expert.

Nuclear translucency and bitest

La translucenza nucale it is a recommended test in all pregnancies, however on its own it is no longer considered sufficient by the guidelines as test at screening for fetal chromosomal abnormalities.

Read also: Prenatal screening, what is the bi-test and how it works

The combined test

«It is instead a method that for this purpose must be integrated with some specific laboratory tests, thus forming the combined first trimester test. In particular, in this test ultrasound is combined with a simple one maternal blood sampling for the search for two proteins of placental origin (free Beta HCG and PAPP-A) ».

“Today, in reality, other tests are also available for estimating the risk of fetal chromosomal abnormalities, in particular those based on fetal DNA circulating in the maternal blood. However, it is my opinion that the bi-test is by no means overtaken by these new methods ».

"There are also other fetal markers in echography (such as nasal bone assessment, fetal venous duct Doppler, tricuspid valve, right fetal subclavian artery location) and other hormone markers (such as placental growth factor or PLGF) that can be analyzed in combination for reduce any suspicions, but which are not always evaluated by the experts ".

Read also: Amniocentesis and villocentesis, the differences

The result of the bitest

The result of the bitest it does not give certainty, "it is a statistical mathematical calculation and it is necessary to understand that each patient has a risk (proportional to age), which can be better defined with this examination. The risk established by the Del Paesena law in order to have free access to additional assessments such as amniocentesis or villocentesis is 1:300. But it is a completely arbitrary cut-off as the perception of risk is a highly subjective element that must be evaluated case by case with the patient ".

What to do if the risk is high

If there is a high risk, “In general, practitioners recommend further examinations. Depending on the outcome of the bitest, the fetal DNA test circulating in the maternal blood, but if there are major anomalies they are indicated invasive examinations like amniocentesis and villocentesis which in these cases can be covered by the National Health System. It is important to know that it is not mandatory to proceed to these examinations, but it is always a choice of the parents ".

Being a statistical calculation, the sensitivity of the combined test (ie reliability), «is del 95%, with a percentage of false positives at the under of 3%". There is also a small percentage of false negatives: "However, even if the risk is low, there remains a residual risk that the fetus is affected by some pathology".

The research continues

The test of translucenza nucale was developed by the research team of Professor Cyprus Nicolaides of King's College Hospital in London as a screening test for the risk of chromosomal and other abnormalities, have recently been proposed new potential for this test.

Uno Danish study, for example, he recently described an association between particularly high nuchal translucency values ​​and the risk of developing autism spectrum disorders. But be careful: we are talking about a research result, to be explored, and in any case only about risk. It does not mean that if the value is high, the child will necessarily have a disorder of this type!

Questions and answers

When can nuchal translucency be done?  

The optimal gestational period for measurement of nuchal translucency is 11 + 0-13 + 6 weeks. The minimum vertex-sacrum length must be 45 mm and the maximum 84 mm

When can the B test be taken?  

The bitest is a test that is performed between the 10th and 14th week of pregnancy and provides information relating to Down syndrome

Read also: Amniocentesis, what it is, how it is performed, when it is done, what risks are involved

  • test at screening
  • combined test
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