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Chromosome Test Results Explained

Types of Chromosome Test

Rapid results
QF-PCR and FISH are molecular tests that can be performed on a CVS sample to provide a rapid but accurate diagnosis of chromosomal disorders. Results take on average three working days. 

Full karyotype
A full karyotype means the laboratory use cells from the sample to look at all the baby's chromosomes under a microscope. They check for any major changes in the chromosomes and can tell the baby's sex. It is a longer process than the rapid tests and results can take up to two weeks.

Array CGH
Genomic microarray (Array CGH) is an advanced method of genetic testing of a sample from CVS or amnio. It can detect copy number changes in a baby's chromosomes. This means it looks for where there are deletions (bits missing) or duplications (where there are extra bits) in the baby's DNA that would not be identified through the full karyotype. It is now sometimes used instead of or as well as karyotyping.

Understanding your results

A Clinical Geneticist will interpret the results of chromosome tests. When tests during pregnancy have shown a chromosome condition the clinical geneticist, if consulted, will discuss the results with you.

Depending on the particular chromosomal condition affecting your baby, you may not always be given the definite answers about what this means, that you are looking for. This is because it is not possible to tell absolutely the impact the condition will have on each child. In some cases the information will be a mixture of the certain, the probable, the possible, and an element of ‘wait and see’.  For example, it may be clear that the baby has trisomy 18 but it is not known if that is complete or a partial form of trisomy 18. It may be possible to see that the baby has a heart defect but it may not be clear how that may affect the baby or whether it is treatable.

Following a diagnostic test result you will need to decide what you want to do next. Only you can make the decision that is right for you and your family. Sometimes it is helpful to talk to someone who has had a similar experience. SOFT have a Befriender service so that you can access via and where you can get support and speak to someone who understands what you are doing through. You can also find more information in the section on Decisions in Pregnancy.


Diagnosis of a related disorder

In some cases babies will be diagnosed with a variation of a Full Trisomic condition, such as a 'Partial' or Mosaicism' diagnosis. More information on these conditions appears in our 'What is Trisomy?' section. 

It can be particularly difficult for health professionals to predict the impact these conditions may have on your baby. Cases involving partial, mosaic and translocation trisomies are rare and therefore very little information exists on exactly how the additional genetic material may impact on the child. 

Mosaicism in particular can be very difficult to diagnose.  Blood cells may show a particular percentage of trisomy cells, skin cells can show a higher or lower percentage, and cells in key organs such as the brain cannot be examined.  Therefore it is almost impossible to predict how much additional genetic material a child with mosaicism has and where that material is located. 

A detailed ultrasound scan can be helpful to show specific abnormalities of organs such as the heart or kidneys, but it is not always possible to predict how severe the effects will be.


What does this mean for my family?

In general, cases of Full Trisomy occur as a de novo mutation in a new baby.  This means that the problem has occurred for the first time in the baby.  They have not inherited the condition from their parents and therefore there is not an associated risk for future pregnancies.

However in some related conditions, such as some partial diagnoses and translocations, there is a possibility they have inherited the condition, in whole or in part from a parent.  

Families facing this type of diagnoses may benefit from a referral to Genetic Counselling services. Genetic Counsellors can pull together all the information about your baby's diagnosis and help translate that for you.  They can arrange for additional testing of parents and/or other family members if that is required.  They can then calculate and advise on the risks of the condition affecting future pregnancies or other family members.  They are trained counsellors and can walk families through information and decision-making processes, to make the decisions that are right for their own family. 



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