What is trisomy 18 in the unborn child?
Trisomy 18, also known as Edwards syndrome, is a serious genetic mutation that is associated with a poor prognosis. The majority of children die before birth. In trisomy 18, chromosome 18 is present in threefold, instead of the usual twofold expression. Girls are slightly more frequently affected by trisomy 18 than boys. In general, the disease is rather rare, occurring with a frequency of about 1:6000.
Causes
Trisomy 18 is a chromosomal aberration. During cell division, a maldistribution of chromosomes occurs, resulting in the triple presence of chromosome 18. Normally, every human being has a so-called double set of chromosomes with 23 chromosome pairs, i.e. 46 chromosomes.
Half of these are from the mother and the other half from the father. However, the germ cells (egg cells and sperm) only have a single set of chromosomes (23 chromosomes). During their formation, the double set of chromosomes is halved.
Thus, when the egg and sperm merge, a cell with a double set of chromosomes can be formed again. The mistake that leads to trisomy 18 can happen both during the formation of the germ cells and only after fertilization. Depending on the time of conception, there are different forms of trisomy 18, and the probability of such a maldistribution of chromosomes increases with the age of the mother. The error that leads to trisomy 18 can happen both during the formation of the germ cells and only after fertilization. The probability of such chromosomal misalignment increases with the age of the mother.
Diagnosis before birth
The suspicion of a trisomy 18 in the unborn child can already arise during ultrasound examinations as part of prenatal care. Signs of this are, for example, delayed growth, malformations of the internal organs or the amount of amniotic fluid. Various blood tests of the mother can be carried out following such suspicions.
However, the triple test only indicates whether there is an increased risk of trisomy. Newer blood tests such as the Panorama Test, the Harmony Test or the prenatal test give specific information about whether a trisomy is present and also which ones. However, a 100% reliable diagnosis can only be made by an invasive examination such as a tissue examination of the placenta (chorionic villus sampling) or an amniocentesis. The cells removed from the placenta can then be examined for trisomy.
