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

Prenatal diagnosis

The Cell‐free DNA screening for trisomy 13,18 and 21 consists in the analysis of DNA fragments from the fetus(es), those DNA fragments being present in the maternal blood during pregnancy.

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

Although it is a genetic test, the aim is not to analyze the genome of the fetus, but only to evaluate the relative proportion of each of the chromosomes 13, 18 and 21 in order to detect an excess of 13, 18 or 21 genetic material when the fetus carries a trisomy 13, 18 or 21.

In practice, this over-representation is tiny, considering that the fetal DNA represents only 10% of the DNA present in the maternal blood.

Next Generation Sequencing (NGS)

This test thus requires a powerful analysis method, the Next Generation Sequencing combined with a high performance computing environnement (bio-informatic pipeline) for quickly analyzing several millions of molecules of DNA, attribute them to their original chromosome, measure their proportion and assess if there is or not an over-representation that is statistically significant.

This is what performs the Cell‐free DNA screening for trisomy 13,18 and 21.

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