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

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

Test ADN fetal en sangre materna. Instituto Bernabeu

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Foetus DNA that is present in the mother's blood can be used to analyse certain chromosomal abnormalities in unborn children.

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 that are analysed in this test are chromosomes 21 (Down's syndrome), 13 (Patau syndrome) and 18 (Edwards syndrome), as well as the sex chromosomes (Turner syndrome and Klinefelter syndrome). 

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. 

A prenatal foetal DNA test aims to obtain the same information as traditional invasive techniques that require amniocentesis or chorionic villus sampling. The test is performed using a source of DNA and it is does not harm the foetus. In short, the main advantage of this type of diagnosis is that it does not pose a risk of any kind to the foetus nor the mother whilst, 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. 

It is a screening test, not a diagnosis. Therefore, if a high risk of chromosomal abnormalities is detected, amniocentesis or chorionic villus sampling is advised. The latter can confirm the suspected diagnosis.