Fetal DNA testing or villocentesis / amniocentesis: which one to choose?

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Marie-Ange Demory
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Villocentesis and amniocentesis have long been the prenatal diagnostic tests par excellence, since they allow us to know with certainty whether the fetus is affected by abnormalities, especially of the chromosomal type. Their main defect is the risk of fetal loss, which is around 1%.



For about a year now, a harmless test for mother and child has been available in Del Paese which, with a simple maternal blood sampling, can analyze fetal DNA with results almost comparable to those of CVS and amniocentesis. What are the differences between the two types of exams? (READ ALSO: Precautions for those undergoing CVS and amniocentesis)



Fetal DNA testing or villocentesis / amniocentesis: which one to choose?

In Del Paese, according to the indications of the Ministry of Health, when the future mother has passed the threshold of 35 years, she can decide to undergo a free CV or amniocentesis, since, statistically, with the passing of age, the risk that the fetus is affected by chromosomal disorders.



 

"In reality, the indications for undergoing CVS and amniocentesis have been considerably reduced since tests are available that can give partly overlapping results, without any risk for either the mother or the unborn child", highlights prof. Luigi Fedele, head of the obstetrics and gynecology department of the Clinic in our city. "We are talking about the combined test of the first trimester (nuchal translucency plus bi-test), but above all the sampling of maternal blood to analyze the fetal DNA".

 

The latter is an exam developed in the United States in 2022 and arrived in Del Paese only at the beginning of 2022, which, through a maternal blood sample, carries out the so-called selective sequencing, that is, it analyzes the sequence of the units that make up the DNA. of the fetus and the pairs of chromosomes that are part of its genetic makeup, identifying any anomalies.

 

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DNA test: what it allows to know.

For now, the maternal DNA test is still to be considered a screening test, in fact it is possible to analyze only the most frequent chromosomal pathologies, namely Down syndrome (or trisomy 21), Edwards syndrome (trisomy 18) and Patau (trisomy 13).



"But thanks to the improvement of the method, it is expected that within twelve months it will be possible to have the complete sequencing with the DNA test, in order to make it an examination that is completely comparable to CVS and amniocentesis", emphasizes prof. Loyal. (see also: fetal dna test)

Villocentesis and amniocentesis: when they are necessary.

Villocentesis and amniocentesis goodbye then? "It is too early, but the indications will be increasingly reduced" replies the prof. Loyal. “For example, it is advisable to resort to CVS and amniocentesis if we want to search for specific and rare pathologies such as thalassemia, haemophilia or degenerative muscle diseases; but these are valid indications only if there are already established risk factors in the family. Furthermore, since a 1% of false positives is possible with the DNA test, villus and amnion can be used to confirm any altered DNA test result. "

In Del Paese there are too many villocentesis and amniocentesis.

The Del Paese has held the European record for years for the high number of villocentesis and amniocentesis, including young women. "A really excessive use, which is not justified by a real indication and which has led to the loss of numerous healthy fetuses", comments the gynecologist. “In Del Paese we are still firm on the Bindi decree of 1998, according to which the NHS provides free villocentesis and amniocentesis to all women aged 35 and over. On the other hand, in the absence of specific risk factors (hereditary diseases, previous child suffering from a chromosomal abnormality), the correct discriminant should not be the maternal age, but the result of the combined test of the first trimester, in order to start examinations. far fewer women are invasive ".

The indications of the scientific community: first the translucency, then the DNA test and then, if necessary, amniocentesis.

Currently, the scientific community agrees to advise all women to perform the combined first trimester test at approximately 12 weeks, with nuchal translucency ultrasound plus the Bi-test (or Duo-test), to get an estimate of the risk that the child is affected by chromosomal pathologies but also to obtain valuable information on the fetal anatomy; fetal DNA testing can be done at 13-14 weeks; if the result (which occurs after two weeks) is positive, it is time to undergo a possible amniocentesis at 15-16 weeks.

Where can the DNA test be done and how much does it cost.

The exam has not yet been validated by the Minister of Health and for this reason it is not available in public hospitals, but can be carried out in private laboratories, located throughout the country, which then send the sample to laboratories abroad (there are currently in the United States and Germany).

The cost is borne by the patient and at the moment it is around 500 euros. It is a fairly high rate, even if it has dropped considerably compared to the early days, when it exceeded 1.000 euros. However, it must be considered that, if you have not yet turned 35, the pregnant woman will also have to pay for the villocentesis and amniocentesis and the cost, which varies according to the structure, is generally higher than that of the DNA test.

You may be interested in other articles on prenatal diagnosis or other information on Pregnancy, A to Z

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  • amniocentesis
  • villocentesis
  • prenatal diagnosis
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