You have been offered a chromosome analysis of your child in order to see whether a chromosome disorder may have caused the stillbirth.
You can read more about the analysis in this pamphlet.
What are chromosomes?
Chromosomes make up the human genetic material. All cells in the body contain 46 chromosomes, 23 from the mother and 23 from the father. Two of the 46 chromosomes are sex chromosomes: Girls have two X chromosomes and boys have an X and Y chromosome. A chromosome is made up of a DNA strand of genes. Genes can be found throughout the DNA strand and are responsible for many different functions in the body.
Chromosome disorders are caused by abnormalities in the genome e.g.
- an abnormal number of chromosomes
- a small piece of a chromosome is deleted (microdeletion)
- a portion of a chromosome is duplicated (microduplication)
What is a chromosome analysis?
Chromosomes can be mapped by examining human tissue. This tissue could be blood or a sample of muscle or other connective tissue.
What is an expanded chromosome analysis - Array CGH (Array comparative genomic hybridization)?
Array CGH is an expanded chromosome analysis which can identify very small changes in chromosomes. This analysis is provided in exceptional cases, such as if a fetus or child dies without known reason.
The analysis is also provided for pregnant women if an ultrasound detects a thick nuchal fold, other anomalies or if the fetus is growth restricted.
The analysis checks for abnormalities in the chromosome material.
All humans can have small changes or deviations in their chromosomes. The majority of these deviations are normal and have no significance. Certain deviations may, however, be pathogenic and these are what the analysis attempts to identify.
How is the chromosome analysis carried out?
A physician will remove a small piece of the child’s achilles tendon. The area of the incision will be covered with a plaster. The tissue sample will be placed in a special liquid and sent to the chromosome laboratory at Rigshospitalet for analysis.
What are the advantages of the analysis?
In some cases, an extended chromosome analysis can explain the death or deformation of a fetus and may indicate whether there is an increased risk of recurrence in a new pregnancy. The analysis from the child may therefore influence any future pregnancies.
What are the disadvantages of the analysis?
The analysis requires a tissue sample from the child. However, the tissue sample from the achillles tendon is very small and is quickly and easily removed.
The extended chromosome analysis can identify even very small deviations in chromosomes. This is an advantage but it also means that we may discover deviations that we do not yet know the significance of. You will always be offered a consultation to discuss this if relevant.
What are limitations of the analysis?
The extended chromosome analysis mentioned above is very detailed and can identify many chromosome deviations. However, it cannot identify all deviations, as we cannot yet examine the entire genome, even with the technologies and knowledge available today. Even if the results come back normal, this does not necessarily mean that the child did not have a genetic disorder.
There can be other reasons for why a child becomes ill and dies, both genetic and non-genetic. These reasons will not be detected by this analysis.
What results can the extended chromosome analysis provide?
- Normal (approx. 85%)
- Chromosomal deviations with known effects which caused a disorder in the child (5-15% )
- Chromosomal deviations with unknown effects (approx. 1%)
- Chromosomal deviations with known effects which did not cause a disorder in the child (”random finding”)(0.5%)
Blood sample from the parents
Approx. 1% of the analyses identify a chromosomal deviation with unknown effects. In these situations, we can examine the parents to see if they have the same deviation. This is done by taking a blood sample from both parents. If the father or mother has the same deviation as the child, then the deviation is most likely not the cause of the child’s disorder or death.
In rare cases, a chromosome deviation in a child can affect other members of the family. In these situations, we will also suggest taking blood samples from the parents.
When will we get the results of the analysis?
You will be given the results of the analysis at a consultation approximately eight weeks after the birth.