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Amniocentesis and CVS: Microarray analysis. Information for Parents
Microarray analysis
Microarray analysis uses modern methods to detect chromosome imbalances too small to see by previous
chromosome tests. Changes in the number or structure of chromosomes can be associated with physical and
intellectual disability in children. Microarray analysis is also called array Comparative Genome Hybridisation (CGH).
Why has microarray analysis been offered to me?
Tests that you have had so far in your pregnancy indicate that there may be an increased risk of a chromosome
abnormality in your baby. Microarray analysis can be used to find a chromosome imbalance in the baby and may
help to explain the ultrasound findings.
What are chromosomes?
Chromosomes are the structures found in the centre of each cell in the body and they contain our genetic
information or genes. Genes are instructions which tell the body how to develop and function. Each cell has 46
chromosomes in 23 pairs. We inherit one of each chromosome from each parent to make a pair. The pairs are
numbered from 1 to 22 from the largest to the smallest. The 23rd pair are the sex chromosomes X and Y. Girls
usually have two X chromosomes (46, XX) and boys one X and one Y chromosome (46, XY).
Testing chromosomes
In the past chromosomes have been looked at with a microscope to detect visible changes in them and this picture
of the chromosomes is called a karyotype. It can identify major chromosome problems but is not able to detect
smaller changes because they cannot be seen with a microscope.
What are the advantages of microarray analysis?
▪ Microarray analysis can detect more chromosome imbalances than previous chromosome tests including some
that are small in size but very significant. When small pieces of chromosome are missing these are called microdeletions and extra pieces are called micro-duplications.
▪ An imbalance in the chromosomes may help to account for ultrasound findings and allow more precise information
to be given about the implications. If you have this test, we will ask for a blood sample from both parents (when
possible) to help interpret the result.
What are the limitations of microarray analysis?
▪ Microarray analysis will not detect very small chromosome imbalances or abnormalities in single genes. Many
genetic conditions are not caused by chromosome imbalances but result from very tiny changes in individual genes
and these are not covered by this test.
▪ Microarray analysis may detect chromosome changes of uncertain significance. This means that either there is not
enough information at present to know if the change is important, or their effects are highly variable and therefore
cannot be used to reliably predict the outcome for the baby. For this reason, genetic laboratories in the UK have
developed a policy to report only on imbalances for which there is clear information.
▪ On rare occasions microarray analysis will identify an imbalance in the chromosomes which is not related to the
ultrasound findings but could have implications for the future health of your baby or other family members. If this
arises you will be offered an appointment with the Clinical Genetics team to discuss the result.
How will I be given the result?
The result will usually be available about 2-3 weeks after the procedure and a Specialist Midwife in the Fetal
Medicine Unit will contact you. If any chromosome imbalances are identified you will be offered an appointment with
the Clinical Genetics Team to discuss the result.
Further questions
If you have further questions about this test, please contact the Specialist Midwife in the Fetal Medicine Unit on
0117 342 5470
University Hospitals Bristol Healthcare NHS Foundation Trust
0117 342 0000 Minicom 0117 94 9869 www.UHBristol.nhs.co.uk
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