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

Patient Space

Your questions

What is the Cell‐free DNA screening for trisomy 13,18 and 21?

This is a brand new prenatal test, reliable and harmless for the fetus. It is performed on a simple blood sample from the pregnant woman.

It determines, with great reliability, if the fetus is affected by a trisomy 13, 18, or 21.

What does the Cell‐free DNA screening for trisomy 13,18 and 21 detect?

This test is based on the analysis of very small amounts of genetic material from the fetus (fetal DNA) which flows out from the placenta to the circulating blood of any pregnant woman during pregnancy.

The fetal DNA is mixed with the DNA of the fetal woman. Using major technological advances in molecular genetics and in bioinformatics, it is now possible to analyze the DNA from the fetus and to determine the number of copies of each chromosome, including chromosomes 13, 18 or 21.

To what extend is it different from other prenatal tests?

Otherprenatal tests exist, like the risk assessment for trisomy 21 using maternal serum markers. The reliability of those tests is very relative since the ratio of false positives is high, thus resulting in the prescription of an amniocentesis for performing a karyotype of the fetus.
Yest, amniocentisis (consisting in the collection of amniotic fluid) is a procedure potentially harmful for the fetus. The risk of induced miscarriage is estimated between 0,5 and 1 % depending on the studies.

The cell‐free DNA screening for trisomy 13,18 and 21 is performed on a simple blood sample from the mother and its reliability is extremely high:

  • Sensibility: 99.1 %
  • Specificity: 99.6 %

Who can get the Cell‐free DNA screening for trisomy 13,18 and 21?

This test is intended only for pregant women at higher risk for fetal trisomy 21. It cannot be performed without a medical prescription or without your informed consent.

When can the Cell‐free DNA screening for trisomy 13,18 and 21 be performed?

It can be performed from the 10th week of amenorrhea (absence of menstruations) and all along the pregnancy.

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 indicates if the fetus is affected or not by a trisomy 13, 18, 21. It is sent exclusively to your doctor who prescribed the test.

He will explain you what the result means and the additional tests that may be prescribed.

What happens in case of negative result?

A negative result means that the presence of a trisomy 13, 18, 21 in the fetus is extremely weak.

Your doctor will go on monitoring your pregnancy, especially by ultrasound scan, and he will tell you if it is necessary to perform additional tests.

What happens in case of positive result?

A positive result means that your fetus is highly probably affected by the trisomy in cause.

Your gynecologist will confirm this result by amniocentesis in order to have a karyotype of the fetus performed.

The karyotype will provide the definitive diagnosis.

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

This test is limited to complete 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.

This test cannot predict late complications of the pregnancy (eclampsia, failure to thrive, premature birth).



Print Top of page