Prenatal Array CGH – Information for Parents

Patient Experience

  • Reference Number: HEY1022/2024
  • Departments: Maternity Services
  • Last Updated: 31 January 2024


This leaflet has been produced to give you general information about the prenatal array CGH test.  Most of your questions should be answered by this leaflet.  It is not intended to replace the discussion between you and your doctor/midwife, but may act as a starting point for discussion.   If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team caring for you.

What is Prenatal Array CGH?

Prenatal array CGH (comparative genomic hybridisation) is a test used to pick up chromosome changes which are too small to be seen by the standard tests available in pregnancy.

What are chromosomes?

Chromosomes are structures which carry genes, and genes are instructions to tell the body how to develop and function. In each cell of our body we have 23 pairs of chromosomes. These are numbered 1 to 22 with the final pair being the sex chromosomes (XX for a girl, XY for a boy). We inherit one chromosome from each parent. Having too much or too little chromosomal material can cause significant problems in development. For instance three copies of chromosome number 21 causes Down syndrome.

Why has array CGH been offered to you?

Ultrasound scans have shown that your baby has an increased chance of having too much or too little chromosomal material. Array CGH is used to see if the baby has a chromosome change which may explain the ultrasound findings. 

What are the advantages of Array CGH?

The main advantage of array CGH is that it can detect very small chromosome changes which cannot be seen by the standard chromosome test. A change in the chromosomes may explain the ultrasound findings and allow more precise information to be given about what this means for your baby.

What are the disadvantages and limitations of array CGH?

Array CGH does not detect all genetic changes. A normal result does not exclude a genetic condition in your baby. Sometimes results can be difficult to interpret and a blood sample from both parents might help to interpret the result.

Are all chromosome changes reported?

Some chromosome results have unclear meaning for the health of your baby. These include:

  • Changes where there is not enough information available to tell the health professionals if it will cause a problem for your baby.
  • Changes that give an increased chance of medical and/or learning problems, but the exact risks are uncertain.

Due to this uncertainty it has been agreed by national experts that some of these changes will not be reported.

Why do some people choose not to have the array CGH?

Array CGH may identify a chromosome change which is not related to the ultrasound findings. It may have implications for the future health of your baby and possibly for other family members. For example, it may show your baby will have an increased risk of cancer later on in life. Some people don’t want to know about these types of chromosome changes.

What happens next?

The first part of the test looks at chromosomes 13, 18 and 21 as these are the most common chromosomes to be associated with ultrasound scan changes. If this test is normal the array CGH test will be done. The result will be available in about 3 weeks. Your Health Professional will contact you when it is available. Occasionally for technical reasons the array CGH is not possible.

If significant chromosome changes are identified you may be offered an appointment with a member of the genetics team to discuss the result.

Should you require any further advice on the issues contained in this leaflet, please do not hesitate to contact the Antenatal screening midwives on 01482382737.

QR code to open leaflet