Non-invasive prenatal diagnosis techniques: testing foetal DNA in the mother’s blood

A chromosomal abnormality detection technique that poses no risk to the foetus

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The foetus DNA present in the mother’s blood can be used to study some chromosomal abnormalities in unborn children. Final del formulario

What is foetal DNA testing in the mother's blood? 

From week 10 of pregnancy on, it is possible to detect foetal DNA in the mother's blood. 

An analysis of this DNA during pregnancy allows us to detect the main foetal chromosomal abnormalities that exist. Human beings have two copies of each chromosome, one of which is inherited from our father whilst the other is inherited from our mother. A foetal DNA analysis allows us to check if a foetus has an abnormal number of chromosomes (aneuploidies). The chromosomes analysed in our most basic test are chromosomes 21 (Down syndrome), 13 (Patau syndrome) and 18 (Edwards syndrome), as well as the sex chromosomes (Turner syndrome and Klinefelter syndrome). In our more complete tests, we analyse the possible aneuploidies, deletions and/or microdeletions and duplications. 

What is foetal DNA testing used for? What is its purpose? 

The aim of non-invasive diagnosis techniques is to use a simple blood sample from the mother to detect the aneuploidies that are most commonly found in embryos. The process poses no risk of foetal loss. 

The prenatal foetal DNA test aims to obtain the same information as traditional invasive techniques based on amniocentesis or chorionic villus sampling, but from a DNA source harmless to the foetus. In short, the great advantage of this type of diagnosis is that it does not involve any risk for either the foetus or the mother, but at the same time being highly sensitive and specific.

What does foetal DNA testing entail? 

A foetal DNA test quantifies the chromosomes that are analysed by sequencing the specific regions in each one (next generation sequencing) and determining if there are two copies of each. 

When is foetal DNA testing advisable? 

This test is recommended in women who have been diagnosed as at risk of chromosomopathies following combined screening during the first term of pregnancy. 

Since this method is absolutely harmless, it is sometimes used when the mother is suffering from stress. 

This is a screening test, not a diagnostic test, so if a high risk of chromosomal alteration is detected, an amniocentesis or chorionic villus sampling is recommended, which will establish the definitive diagnosis.

Results may take 7 to 12 working days to be ready, depending of the complexity of the test performed.