As a woman ages, the chromosomes are increasingly incorrectly distributed in the egg cells, which is why older women become pregnant less often and there is a high rate of miscarriage.
The woman’s egg cell has to halve its chromosome number in order to be able to absorb the chromosomes of the male sperm cell.
Polar bodies are small round appendages found on the outer shell of the egg cell, in which the chromosomes filtered out during maturation are located (like waste bins).
We examine these ‘waste bins’ of the egg cell for missing chromosomes. If we find that, for example, chromosome 21 is missing in the polar body, we know that the embryo will not implant or that a child with trisomy 21 (Down Syndrome) may be produced.
In polar body diagnosis, DNA probes are used that bind to particular parts of the chromosomes. The DNA probes are marked with various fluorescent dyes in order to be visible under the microscope. We recognise the number of copies of in this area in the cell nuclei from the number of signals for the respective segment of chromosome.
The polar body diagnosis can unfortunately only be used for a limited selection of chromosomes. The number of chromosomes 13, 16, 18, 21 and 22 can currently be determined using this method.
Following a polar body diagnosis, the normal risk remains. This means that there may be other chromosomal abnormalities that are not detected.
It is also possible that the male sperm cell has a faulty set of chromosomes, or that a chromosomal change in the embryo does not occur until after fertilisation.
The examination is therefore not a substitute for the amniotic fluid examination. In the case of pregnancy, a prenatal chromosome examination on the embryo in Linz is recommended.