Fetal DNA Test: The non-invasive prenatal screening exam
The fetal DNA test is a prenatal screening test aimed at assessing the risk that the fetus may have some chromosomal abnormalities indicative of diseases such as trisomy 21 or Down syndrome. This non-invasive prenatal diagnosis is made by taking maternal blood.Discover with us everything there is to know about fetal DNA testing! First, however, here is a video on how to manage insomnia in pregnancy:
What is the fetal DNA test?
The fetal DNA test is a screening test, which means it assesses the risk that there may be chromosomal abnormalities in the fetus. If the Combined Test offers a diagnosis with an accuracy of about 90%, the fetal DNA test can reach even 99% accuracy in its result, thus decreasing the risk of being wrong about the presence of chromosomal pathologies such as trisomy 21 (the down syndrome).
The fetal DNA test is not invasive: to perform it, in fact, a simple maternal blood sample is enough. In fact, in maternal blood, fragments of fetal DNA are found: the placenta releases a small amount of free fetal DNA circulating in the mother's blood that a "special technical instrumentation will be able to separate from the maternal DNA. The test analyzes the DNA. fetal free to evaluate the risk that the fetus may present trisomy 21 (Down syndrome), trisomy 14, trisomy 18, chromosome 22 microdeletion syndrome or other anomalies such as the alteration of the number of sex chromosomes.
The result of the screening test will be able to assess whether the risk of the presence of these chromosomal alterations is high or low, obviously remembering that it is always a probability calculation (however accurate) and not an "absolute certainty."
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What can the test evaluate?
The fetal DNA test allows to evaluate the risk of different chromosomal alterations in the fetus, starting from trisomies. It is particularly useful for the prenatal diagnosis of trisomy 21 or Down syndrome. If the test gives a low-risk result, it means that the chance that the child may have Down syndrome is about 1 in 10,000. If the risk is high, the probability of trisomy will be equally high, so - if desired - it will be good to proceed with an invasive examination such as amniocentesis or CVS to confirm it.
The fetal DNA test also allows you to evaluate the sex chromosomes, which allows you to know the sex of the fetus as early as the tenth week of pregnancy, obviously if desired. The objective of examining the sex chromosomes is rather that of evaluating possible alterations in their number. This kind of anomalies - it must be specified - does not lead to any type of disability or malformation, but could lead to some clinical manifestation linked to the development of learning, pubertal development and / or fertility.
The DNA test also makes it possible to assess the risk of the presence of a "syndrome other than Down syndrome, that is the microdeletion syndrome of chromosome 22, much rarer (affects about one child in two thousand). This syndrome can lead to cardiac malformations or cognitive-behavioral disorders, in some cases it is even asymptomatic.
How reliable is it?
The fetal DNA test has a very high reliability, especially with regard to Down syndrome: if the test diagnoses the presence of this anomaly, its reliability will be greater than 99%. False positives are indeed very rare. Despite this, however, if the result is positive it is usually recommended to proceed with an examination such as amniocentesis or CVS.
The combined test cannot boast of such high reliability, which is why the fetal DNA test is usually recommended to those who have found uncertain results with nuchal translucency and bitest. Finally, according to the Ministry of Health, the reliability of the fetal DNA test for trisomy 18 is 96%, while for trisomy 13 it is estimated at 91%.
- Mangiagalli Polyclinic
- Veronesi Foundation
