Karyotype examination: what it is and how it takes place

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Catherine Le Nevez
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Karyotype examination

Il chromosome kit (karyotype) of an individual derives 50% from the mother and 50% from the father. Every human being has 46 identical chromosomes in his DNA (divided into 23 pairs of identical chromosomes) 22 of which are XX, while the last couple establishes the sex of the subject (XX for the woman, XY for the man. conception a sperm with 23 chromosomes merges with an egg with 23 chromosomes to give life to a human being with 46 chromosomes.





This premise serves to understand what the karyotype examination is for and how it takes place.

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Before conception

 



The karyotype examination consists of a simple blood collection by both intended parents and in an analysis chromosomal. If done before a pregnancy, this test allows to verify the existence of chromosomal anomalies in the karyotype of the parents, anomalies that could come passed on to the child and causing genetic diseases, such as cystic fibrosis, thalassemia or chromosomal diseases such as Down syndrome.
It is generally recommended before conception for couples in which one of the two partners (or both) are carriers of hereditary diseases and are likely to pass it on to their child.

Pregnancy: the special tests to do

During pregnancy

 

The examination of the karyotype of the fetus can then be carried out during pregnancy, through more invasive tests, such as amniocentesis or CVS, to determine the presence of chromosomal anomalies such as to cause diseases or malformations.

These exams are recommended for all women who have passed the 35 years because after this age the probabilities of fetal chromosomal abnormalities increase (in 96% of cases it is trisomy 21, 18, 13, X, Y).

Currently, the ministerial guidelines require the woman to first undergo the combined test (blood test and nuchal translucency) around the 10-13th week to establish the percentage of risk and in the event of a positive result, the woman will be granted access to the amniocentesis free of charge in a public hospital.

Read also: Calendar of exams to do in pregnancy

But theamniocentesis it can also be done privately. The examination must be done between the 15th and 17th week of gestation and consists in taking a sample of amniotic fluid which will then be analyzed in detail from the point of view of the karyotype.

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La villocentesis (chorionic villus sampling), on the other hand, must be done between the 10th and 12th week and involves taking a sample of cells from the placenta.
The examination will reveal any anomalies and the baby's sex: in fact, the number of chromosomes and sex chromosomes will be read in the report.
Both tests, CVS and amniocentesis, involve a percentage, albeit low, of risk of abortion spontaneous.
 

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