Cell-free DNA screening
for trisomy 13, 18 and 21

Healthcare Professional Space

Your questions

The Cell‐free DNA screening for trisomy 13,18 and 21 is it performed at Laboratoire CERBA?

The Cell‐free DNA screening for trisomy 13,18 and 21 is indeed performed in France since November 2013 at Laboratoire CERBA.

Laboratoire CERBA has a long experience in prenatal diagnosis. It was the first laboratory in France to offer routine diagnosis for fetal sex and Rhesus D.

A large scale clinical trial is currently carried out and the first results are in line with all international studies.

What are the indications of the Cell‐free DNA screening for trisomy 13,18 and 21?

The Cell‐free DNA screening for trisomy 13,18 and 21may be proposed to every woman in the following situations:

1. Primary detection (serum markers not performed)

2. After maternal serum screening:

Screening strategy:

  • 1st trimester maternal combined screening
  • 2nd trimester maternal integrated screening
  • 2nd trimester (serum markers only)

Risk:

  • High (>1/250)
  • Intermediary (1/250-1/1000)
  • Weak (< 1/1000)
  • Serum markers out of range (MoM PAPP-A <0,25 or >2,5 and/or MoM hCG <0,25 or >5)

3. Patient with prior medical history of fetal aneuploidy

4. Parental robertsonian translocation involving a chromosome 13 or 21

5. Maternal age 35 years or older (or according to local recommendations)

6. Twin pregnancy, without increased nuchal translucency or other abnormalities at ultrasound scan

However, this test must not be proposed to date.

  •  This test should not be proposed in case of signs at ultrasound scan (including nuchal translucency equal or above 95th percentile) due to a risk around 2,5 % of unbalanced abnormalities other than the ones detected by this assay ;
  • This test is not recommended for other chromosomal abnormalities(microdeletion syndrome, sexual chromosome abnormalities, other unbalanced chromosomal abnormalities)

In which cases the Cell‐free DNA screening for trisomy 13,18 and 21 is not recommended?

In case of signs at ultrasound scan (including nuchal translucency equal or above 95th percentile) due to a risk around 2,5 % of unbalanced abnormalities other than the ones detected by this assay

Till when in the pregnancy can the Cell‐free DNA screening for trisomy 13,18 and 21 be performed?

Th Cell‐free DNA screening for trisomy 13,18 and 21 is validated for women at increased risk of trisomy 21, from the 10th week of amenorrhea.

What about the reliability of the test?

The sensitivity and specificity of the test are both greater than 99% for trisomies 13, 18 and 21.

Can this test be performed in first intention?

It is not recommended to perform this test in first intention.

The test in indicated in the following situations :

  1. Patient with an increased risk of trisomy 21 after maternal serum screening, regardless the strategy used, without nuchal translucency (nuchal translucency below the 95th percentile).
  2. Patients belonging to a group at increased risk in the absence of any sonographic sign:
    • Patients with prior medical history of fetal aneuploidy.
    • Parental robertsonian translocation involving a chromosome 13 or 21.
  3. Maternal age 35 years or older (or according to local recommendations), in the absence of nuchal hypertranslucency or other sonographic abnormalities.
  4. Twin pregnancy, without increased nuchal translucency or other abnormalities at ultrasound scan.

What are the limits of the test?

  • This test must not be confused with the fetal karyotype, obtained after a biopsy of chorionic villi or and amniocentesis, which provides additional information.
  • This test is limited to complete and homogenous trisomies 13, 18 and 21. Chromosome abnormalities like balanced translocations, deletions and duplications are not detected.
  • This test does not detect genetic diseases like cystic fibrosis.
  • This test does not detect anomalies of incomplete closing of the embryonic neural tube like spina bifida.
  • This test cannot predict late complications of the pregnancy (eclampsia, failure to thrive, premature birth).

How long does it take to get the result?

The result of the test is available within 15 working days after reception of your sample by Laboratoire Cerba.

How is the result delivered?

The result report is sent directly and solely to the gynecologist who prescribed the test.

Over-the-phone support is provided by the clinical pathologists in charge of the test at Laboratoire CERBA, especially for reminding the limits of the test and the current recommendations in case of a pathological result.

What should be done in case of negative result?

A negative result does not exclude a pathological pregnancy (false-negative); its sensitivity and specificity are greater than 99% for trisomies 13, 18 and 21.

Therefore, the sonographic monitoring of the pregnancy must be continued.

What should be done in case of positive result?

Although the sensitivity and specificity are greater than 99% for trisomies 13, 18 and 21, a positive result does not necessarily imply that the fetus is affected.

Therefore, a control by fetal karyotype  from a biopsy of chorionic villi or from a puncture of amniotic fluid is mandatory in order to confirm the result and to elucidate the chromosome mechanisms

Are there specific guidelines for sample collection?

The sample must be collected on special tubes (Streck) provided by Laboratoire CERBA.Those tubes may be ordered from the local agent of Laboratoire CERBA.

Please contact your local agency for any request regarding equipment for sample collection: Download local agency

The following guidelines must be observed:

1. Identify the 2 « Streck » tubes provided..

2. Collect 2 x 10 ml whole blood. The 2 tubes must be completely full.
Caution: tubes must be filled slowly.

3. Mix the tube by gently reverting them at least 10 times.

4. Both tubes must be inserted in a « refrigerated » sample bag.

5. Store the bag containing the 2 tubes between + 4° C and + 8° C.
   The transport will occur at refrigerated temperature.
   THE SAMPLE MUST BE DELIVERED TO LABORATOIRE CERBA WITHIN 48 HOURS:

6. DO NOT FREEZE

7. The following documents must come with the sample and be inserted in the dedicated side pocket of the sample bag:

  • Test request form.
  • Medical information certificate and informed consent form.
  • Report of ultrasound scan at first trimester.
  • All required documents depending on the indication.

Storage of “Streck” tubes prior to use:

  • At room temperature till the expiration date mentioned on the tube
  • Do not freeze the tubes


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