Non-invasive prenatal test

non-invasive prenatal test

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What is non-invasive prenatal testing?

Non-invasive prenatal testing is a method of detecting certain chromosomal abnormalities in the fetus. Also called non-invasive prenatal screening, these tests are reliable, fast and accurate. For the detection of Down syndrome, Edwards’ syndrome and Patau’s syndrome the overall sensitivity is 99%.

The test requires DNA from the mother and fetus, which is obtained from the mother’s blood. This is tested to find out if there is a risk that the baby may have some chromosomal problems such as trisomy 13 or 18, or Down syndrome. This test can also find out the sex of the baby.

It is recommended that pregnant women at least 10 weeks pregnant should have this test. They should also be properly informed about the options, benefits and limitations of first and second trimester screening and diagnostic tests. It is a professional who should talk to the patient and tell her whether, in her case, noninvasive prenatal testing would be beneficial. He or she will also help interpret the results.

What does the non-invasive prenatal test detect?

There are 2 non-invasive prenatal tests. Performing one or the other depends on the abnormalities you want to test for:

With the Aneuploidy test CR. 13, 18, 21, X, Y the following fetal aneuploidies are studied:

  • Down syndrome (trisomy 21). It is the most frequent disease of this type. Those born with Down syndrome may have gradual intellectual disability (mild to moderate), heart defects and other disorders.
  • Edwards’ syndrome (trisomy 18). This disease causes a high rate of miscarriages. Affected babies usually have severe malformations and mental retardation. They usually do not survive more than one year.
  • PPatau syndrome (trisomy 13). As with Edwards’ syndrome, Palau syndrome is also associated with a high number of miscarriages. This disease causes severe mental retardation and there is a possibility of severe congenital cardiac malformations, as well as other pathologies. They also do not usually survive beyond one year.
  • Alterations in the number of sex chromosomes. In females it would be Turner syndrome (45,X) which means the absence of an X chromosome. In males, Klinefelter syndrome (47,XXY), which would mean the presence of an extra copy of the X chromosome.

The Aneuploidy test CR. 13, 18, 21, X , Y + all chrom + microdeletions is an additional test that analyzes rare and small size alterations (microdeletions) that appear in the chromosomes, as well as aneuploidies in all chromosomes. Translated with www.DeepL.com/Translator (free version) 13, 18, 21, X , Y + all chrom + microdeletions is an additional test that analyzes rare and small size alterations (microdeletions) that appear in the chromosomes, as well as aneuploidies in all chromosomes.

When are the results delivered?

The results of the Aneuploidy test CR. 13, 18, 21, X , Y Aneuploidy test results are delivered in 7 working days CR. 13, 18, 21, X , Y + all chrom + microdeletions is an additional test that analyzes rare and small size alterations (microdeletions) that appear in the chromosomes, as well as aneuploidies in all chromosomes. Translated with www.DeepL.com/Translator (free version) 13, 18, 21, X, Y + all chrom + microdeletions take 15 working days.

How are the results interpreted?

If the test concludes with a ‘negative’ or ‘low risk’ result, it is very unlikely that the fetus has one of the detectable trisomies (21, 18 and 13). As mentioned above, there are occasions when some microdeletion syndromes are also tested and the sex chromosomes (X and Y) are studied.

There is a possibility, however, that the test may give a false positive. This means that it would be possible for the baby to have a chromosomal alteration even if the result is low risk. It should be remembered that fetal DNA in maternal blood is a screening test, not a diagnostic test. Moreover, this test has its limitations: it does not evaluate all chromosomes and does not detect many alterations caused by small changes in DNA. There are other chromosomal or genetic diseases that the test cannot detect.

If the test result is ‘positive’ or ‘high risk’, the fetus has a high probability of having a chromosomal abnormality. However, although the ability of the test to detect Down syndrome is quite high, it is not good enough to identify abnormalities of other chromosomes (18, 13 or X). It is necessary to remember in these cases the possibility of false positives.

As we have seen, there are several non-invasive prenatal screening tests. Health professionals are the only ones in charge of offering genetic counseling before the test and after obtaining the results. If doubts arise, it is advisable to refer the pregnant woman to a specialist.

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