Fetal nuchal translucency test

Nuchal translucency – what is it?

Nuchal translucency is defined as subcutaneous fluid accumulation in the neck region of the fetus. It is one of the components of a combined test that also includes the concentration of beta-hCG and PAPP-A protein, as well as other parameters such as fetal heart function. The fetal nuchal translucency test is performed to assess the risk of chromosomal abnormalities, including the most common, Down syndrome.

Nuchal translucency test in fetus – what does it look like?

The nuchal translucency test is performed by the gynecologist during the first trimester ultrasound examination. In order to accurately examine nuchal translucency, the specialist must visualize the baby’s head and the upper part of the chest in the sagittal section plane on the screen with the appropriate magnification. The greatest distance between the skin and soft tissue is then measured at the level of the baby’s cervical spine. In order for the examination to be performed and interpreted well, it must be performed at specific weeks of gestation, having previously determined gestational age based on parietal length.

The fetal nuchal translucency test is part of a composite test. For this reason, after the measurement and biochemical tests, the risk of the most common chromosomal defects for a particular woman is calculated. Depending on the result, the expectant mother may be referred for further diagnostic testing, which includes a non-invasive NIPT test or invasive tests such as amniocentesis. With these, the result can be ruled out or confirmed with almost 100 percent certainty.

Nuchal translucency test in fetus – when should it be done?

Nuchal translucency is part of the mandatory ultrasound examination in pregnancy, which is performed between the 11th and 14th week of pregnancy. Due to the procedure (and purpose) of the examination, some refer to it as “genetic ultrasound”.

Nuchal translucency test in fetus – standards

The result of fetal nuchal translucency is related to the gestational age according to the centiline grid. That is why it is so important to accurately determine the gestational age and perform the examination at the weeks recommended by specialists. It is also considered that fetal nuchal translucency examination alone is not sufficient to determine the risk of chromosomal defects in the child.  

The standard for nuchal translucency is less than 2.1 mm at week 11, when the baby’s parietal and sitting length is 45 mm, and less than 2.7 mm at week 14 (13+6), when the parietal and sitting length is 84 mm. If the fetal nuchal translucency test indicates a result greater than 3.5 mm, this is an indication of a more advanced diagnosis.

Fetal nuchal translucency test – wrong result

Es ist wichtig, daran zu denken, dass sowohl der Transparenztest als auch der Komposittest Screening-Tests und keine Diagnosetests sind, so dass ihr Ergebnis möglicherweise weiter überprüft werden muss. Liegt das durch den kombinierten Test ermittelte Risiko unter 1:1000, wird eine weitere Ultraschalluntersuchung im zweiten Schwangerschaftstrimester (zwischen der 18. und 22. Schwangerschaftswoche) empfohlen. Liegt das Ergebnis des kombinierten Tests im mittleren Bereich, d. h. das Risiko liegt zwischen 1:300 und 1:1000, wird ein kostenloser fetaler DNA-Test empfohlen. Im Falle eines hohen Risikos (>1:300) sollte die Schwangere gemäss den aktuellen Empfehlungen an einen Spezialisten für Perinatologie oder klinische Genetik überwiesen werden, um über eine mögliche weitere Diagnostik zu entscheiden.