2023-04-19 09:25:36
What is nuchal translucency?
Nuchal translucency corresponds to a small area located at the neck of the fetusdue to a detachment between his skin and his cervical spine,
Aurélie Kaczmarek: Nuchal translucency is a completely physiological – therefore normal – edema that all fetuses have between 9 SA and 15 SA, so during the first trimester.
This area is said to be anechoic, which means that it does not reflect ultrasound in the form of echoes and therefore appears black on ultrasound.
All fetuses therefore present with nuchal translucency on ultrasound during the first trimester, which disappears therefollowing. Nuchal translucency testing is important because it can detect several health problems : genetic abnormalities, heart defects or disabilities.
Can trisomy 21 be seen on first trimester ultrasound?
Trisomy 21, also called syndrome de Downis one of the most common chromosomal abnormalities with one in 700 live births.
This genetic abnormality not seen directly on ultrasoundbut the observation of the latter associated with the results of blood tests, makes it possible to evaluate the risks that the fetus is affected or not.
The nuchal translucency examination is thus essentially used to assess the risk of trisomy 21. “Be careful, however, nuchal translucency is only one indicator among others, and its analysis alone does not make it possible to make a diagnosis ! “recalls the specialist.
In addition to this nuchal translucency, a blood test – called assay of serum markers – is systematically offered to the patient for a more precise calculation of the risks of trisomy 21. origins, tobacco etc.), will allow a more precise assessment of the risk of trisomy 21” explains the midwife.
If the nuchal translucency measurement is done systematically and obligatory, the blood test is offered to the future mother who is free to accept it or not.
When this nuchal translucency examination is combined with a blood test, the detection rate is 90%.
12 weeks of pregnancy or 13 weeks of amenorrhea: when to do the nuchal translucency test?
For it to be correctly interpreted, the nuchal translucency examination must imperatively be done between the 11th week of amenorrhea (SA) and the 13th SA + 6 days. “It is essential to be very precise, because everything is decided one dayand if the measurement is taken too early or too late, it cannot be interpreted” insists the sonographer midwife.
The cranio-caudal measurement confirms that the patient is in the right period to take the measurement. It is indeed common for patients’ cycles to be irregular, and for the calculated fertilization date to be imprecise.
Aurélie Kaczmarek: To be certain that the patient is between 11 weeks and 16 weeks + 6 days, the cranio-caudal length must be between 45 and 84 mm.
If the fetus is smaller, the patient should return for an ultrasound for a new nuchal translucency measurement.
Where to do the nuchal translucency ultrasound?
The first trimester ultrasound, during which the nuchal translucency is measured, can be done at any gynecological and obstetrical ultrasound practice.
Normal Values: How Much Should Nuchal Translucency Measure?
Nuchal translucency, measured between the 11th SA and the 13th SA + 6 days, must be less than 3mm.
Thick or raised, low or thin nuchal: When to worry regarding nuchal translucency?
As soon as the nuchal translucency is greater than 3 mm, the risks of genetic abnormality are greater. Depending on the results of the nuchal translucency combined with those of the blood test, the doctor or midwife will then suggest additional examinations to the patient: trophoblast biopsy, choriocentesis or amniocentesis. These examinations each presenting risks of miscarriage, the patient is not required to accept them.
“The nuchal translucency cannot be too fine, so there is no normal minimum value” adds Aurélie Kaczmarek.
We also note thata nuchal translucency greater than 3 mm is not a diagnostic element. “A thick nuchal translucency may not be associated with trisomy 21, and conversely, it happens that a fetus is a carrier of trisomy 21 and that its nuchal translucency is normal”, underlines the midwife sonographer.
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