Definition – what is a trisomy 13 in the unborn child?
Trisomy 13, also called Pätau syndrome, is a change in the chromosomes in which chromosome 13 is present three times instead of twice. The disease is accompanied by malformations of several internal organs and can in many cases be detected before birth. Children born with trisomy 13 rarely live longer than six months. Trisomy 13 occurs in about 1 in 10,000 children.
Causes
The cause of trisomy 13 is in most cases a defect in the eggs or sperm cells. These cells normally have half a set of chromosomes with 23 chromosomes. In the following fertilization, the union of the egg and the sperm creates a cell with a whole set of chromosomes, i.e. 46 chromosomes.
In trisomy 13, there is an error in the separation of the chromosomes in the egg or sperm cells, so that chromosome 13 is duplicated. Accordingly, after fertilization, chromosome 13 is present three times. This is called trisomy. An exact cause for this error in the distribution of chromosomes could not be determined so far. A possible risk factor is a higher age of the mother at fertilization.
Diagnosis before birth
In most cases, trisomy 13 can be diagnosed before birth as part of prenatal care. During the ultrasound examination, the so-called neck wrinkle measurement is performed as standard. The nuchal fold is an accumulation of fluid under the skin in the area of the neck in the unborn child.
From a thickness of about 3mm it is called thickened. A thickened nuchal fold can be an indication of a number of diseases such as trisomy 21, 18 and 13. If this examination is conspicuous, a series of further examinations follow.
These include an examination of the amniotic fluid as well as taking a sample from the placenta. From these samples, fetal cells can be obtained for chromosome analysis. The chromosome analysis provides information whether a trisomy is present or not. Besides the above mentioned invasive examination methods, which always carry the risk of miscarriage, there are also non-invasive blood tests such as the Harmony test to detect trisomy.
