A karyotype test is basically a test that analyses your chromosomes. It tells you how many chromosomes a person has and looks at the structure of each chromosome individually and allows us to determine whether your embryos need additional screening before they are selected for implantation.
A karyotype can be performed on any tissue but most often it is done from a blood sample, a sample of amniotic fluid or a piece of placenta obtained through chorionic villi sampling. Karyotyping is a complex process that involves growing the cells, obtaining the chromosomes, staining and analysing the chromosomes and reporting the results. A karyotype is an actual photograph of the chromosomes from one cell.
We check the chromosome set of both partners to exclude the possibility of underlying chromosomal rearrangement problem and, from the patient’s perspective; a karyotype is usually a simple blood test. It is what happens to the blood after it is collected that is actually quite complex.
Sometimes a part of one chromosome gets detached and attached to another chromosome. This does not cause any apparent abnormality in the parent as the total set of the chromosomes (DNA) is complete. However, if the parent cell has a chromosomal rearrangement problem the DNA material will split unequally. The egg or the sperm will either miss or carry an extra part of a chromosome and the resulting embryo will not be chromosomally normal. This embryo either fails to implant or results in a miscarriage or a chromosomally abnormal child.
If this chromosomal rearrangement problem is diagnosed beforehand, through the use of karyotyping, we can test for it in the embryos and choose only normal embryos for transfer. This is known as ‘pre-implantation genetic diagnosis (PGD).