Fetal nuchal translucency test

Nuchal translucency – what does it consist of?

Fetal nuchal translucency testing is one of the non-invasive prenatal tests that is performed during a first trimester ultrasound. Assessment of nuchal translucency involves measuring the fluid accumulated around the fetal neck. The doctor performing the 2D ultrasound exam checks the skin fold where the “reservoir” of fluid is located. If the amount of fluid is too much, the fold will enlarge at the same time. This can mean that the circulatory system is overloaded, indicating the onset of a genetic disease, among other things. Down syndrome.

It is worth noting that the negative results shown by the fetal nuchal translucency test do not necessarily indicate a disease. To confirm the diagnosis, the doctor will refer the pregnant woman for additional tests, such as the PAPP-A test. Free fetal DNA testing can also be performed. The recommendations of the Polish Society of Gynecologists and Obstetricians clearly indicate that only a full range of diagnostic genetic tests performed in the appropriate prenatal period, that is, in the first trimester, can give confirmation of the diagnosis related to the genetic burden of the child and the presence of chromosomal defects.

Fetal nuchal translucency test – norms

Nuchal translucency in a healthy baby should not exceed 2.5 millimeters between the soft tissues and the skin. Nuchal translucency measurements indicating abnormalities must exceed 2.9 millimeters. On the other hand, an increased risk of genetic diseases occurs when the fetal nuchal translucency test gives parameters between 3 and 4.5 millimeters. However, it is worth noting that increased risk is not synonymous with 100% diagnosis. As many as about 70% of children whose nuchal translucency closed at 4.5 millimeters are developing normally. However, a nuchal translucency test that shows more than 5 millimeters already indicates fetal defects and genetic diseases in most cases. However, the mother-to-be still needs to confirm the diagnosis with the PAPP-A composite test.

What does the PAPP-A test consist of? Course of the study

The PAPP-A test is sometimes referred to as a duplicate test. It allows assessment of the concentration of PAPP-A protein, which is a protein synthesized in the trophoblast that has an immunosuppressive function. In addition to it, the level of the free subunit of chorionic gonadotropin, or more specifically beta-hCG. The Polish Gynecological Society recommends that the PAPP-A test be performed simultaneously with the assessment of nuchal fold translucency by ultrasound (ultrasound).

The PAPP-A test is classified as a non-invasive method, which means that it does not interfere with the fetal environment. As a result, it is completely safe and has no risk of miscarriage. The test involves drawing a small amount of maternal blood from the elbow vein, which is then submitted for laboratory analysis. Importantly, the mother-to-be does not need to be fasting – the PAPP-A test will indicate a reliable result regardless of the food consumed.

What are the standards for the PAPP-A test?

Like most tests, the PAPP-A test also has designated standards that help specialists in diagnosis.

• The increased risk of having a child with Down syndrome may be evidenced by the results:
  • Reduced concentration of PAPP-A protein (less than 0.5 MoM);
    elevated beta hCG hormone (above 2.52 MoM);
  • Elevated nuchal translucency index.

• An increased risk of having a baby with Edwards or Patau syndrome may be indicated by the results:
  • Reduced concentration of PAPP-A protein (less than 0.33 MoM);
  • reduced levels of beta hCG hormone (less than 0.33 MoM);
  • Elevated nuchal translucency index.

Nuchal translucency and PAPP-A test – why should they be performed?

Prenatal tests, which include the PAPP-A test and the fetal nuchal translucency test, are designed to detect early the risk of genetic or developmental defects in the baby. With their help, it is possible to plan appropriate treatment (while the pregnancy is still in progress or immediately thereafter) and prepare Parents for the possibility of raising a child who will require special care.

When can nuchal translucency testing and other prenatal tests be performed?

Fetal nuchal translucency testing and other prenatal tests, such as the PAPP-A test, are performed between 11 and
14 weeks of pregnancy
, that is, in the first trimester. It is recommended that the PAPP-A test be done at the same time as an ultrasound, during which the doctor assesses nuchal translucency. Performing two tests simultaneously increases their reliability.

An ultrasound to measure nuchal translucency is completely safe for both mother and baby and must necessarily be performed between 11 weeks and 14 weeks of pregnancy (up to the 6th day of the 13th week of pregnancy). It is only at this time that it is possible to assess the risks associated with the enlargement of the fold volume from the fetal neck area.

Elevated nuchal translucency test result – what next?

What are the indications for an elevated nuchal translucency result? First of all, a PAPP-A test is performed, and if it confirms the diagnosis resulting from the ultrasound, the mother-to-be is referred for an amniocentesis test. In this case, however, we are talking about an invasive procedure that involves the collection of amniotic fluid from the abdominal layers. It is worth noting that this method gives virtually 100% certainty of the presence or absence of a genetic defect. In the second situation – if the disease is not aired, it may indicate a heart defect, so the doctor in charge of the pregnancy recommends a heart echo and a thorough midline ultrasound.

What diseases does the fetal nuchal translucency test detect?

Fetal nuchal translucency testing helps detect conditions such as:

• Down syndrome,
• Edwards syndrome,
• Patau syndrome,
• Di George syndrome,
• fetal heart defects.

It is worth noting that the most frequently detected condition is Down syndrome. At the same time, this disease gives the best prognosis related to fetal and child development – the average life expectancy of people with Down syndrome is 49 years. In contrast, other genetic defects are associated with multiple organ failure, which at best can give a child a year to live. Other prenatal tests are used to detect other defects.

Nuchal translucency and PAAP-A test – reimbursement and price of the test

Nuchal translucency testing and the PAPP-A test are recommended for every pregnant woman, regardless of her age or other factors. However, these are paid studies. Their price ranges from 250 to 400 zlotys. However, costs may vary from lab to lab.

Prenatal testing reimbursement is available to women who are in the risk group. They are covered by the National Health Fund program when:

• Are more than 35 years old,
• Have given birth to a child with a birth defect,
• have received abnormal ultrasound results,
• Are burdened with a genetic defect,
• there was a genetic defect in the partner’s family.

FAQ:

• What is nuchal translucency testing?

The nuchal translucency test is performed during a non-invasive ultrasound. The doctor checks the distance of the soft tissue from the skin. This is because there is a “reservoir” of fluid on the neck of the fetus. Too much fluid can mean a genetic defect.

• What are the norms in nuchal translucency testing?

In a healthy baby, the translucency closes at 2.9 millimeters. The risk of genetic disease is associated with an increase in this parameter of 3 to 4.5 millimeters. However, despite this, about 70% of children with this result develop normally. A result of more than 5 millimeters is already a high risk of defect.

• What diseases does the nuchal translucency test detect?

Elevated nuchal translucency may initially indicate diseases such as:

• Down syndrome,
• Edwards syndrome,
• Patau syndrome,
• Di George syndrome,
• fetal heart defects.