Prenatal CGH Array

An array CGH is indicated by a gynaecologist in one of the following cases:

• Abnormal ultrasound findings, e.g. organ malformation in combination with growth retardation or multiple malformations.
• Abnormal chromosomal findings that need to be further clarified.
• History of chromosomal abnormalities in the family.
• Family history of increased risk of developing abnormalities.
• Repeated miscarriages.

We also perform array CGH if the prospective parents have a great need for reassurance and want very detailed information about the chromosomal picture of the foetus.

The test can be done on DNA from cells obtained by:

• Amniocentesis: from 15 weeks gestation onwards
• Chorionic villus sampling: from 12 weeks gestation onwards

Cytogenetic analysis or conventional karyotyping is used to determine that the number, size and shape of an individual’s chromosomes are correct. This test is performed to rule out major alterations associated with problems such as miscarriages, malformations and/or mental retardation. 

The main difference between the two tests is their resolution.

• The resolution of conventional karyotyping or cytogenetic analysis is limited and can only detect changes in the number and/or structure of chromosomes larger than 5-10 million base pairs (Mb).
• The resolution of array CGH or molecular karyotyping is much higher, as it allows the simultaneous detection of very small alterations (gains or losses of DNA fragments) responsible for more than 300 genetic syndromes associated with mental retardation, autism, heart disease and other pathologies, most of which are not detectable by conventional karyotyping.

• Positive or altered result: indicates the presence of a chromosomal abnormality. However, sometimes it may not be known whether the abnormality detected may be the cause of the abnormal ultrasound findings or what consequences it may have on the baby’s health. An additional blood test is then recommended for the parents. If a healthy parent carries the same change in the genetic material, it can usually be assumed that this variation is of no health significance.
• Normal or negative result: indicates that no chromosomal abnormality has been detected by this technique. It should be noted that there are some genetic diseases that cannot be diagnosed by array CGH, such as those caused by differences in DNA that are too small to be detected even by array CGH. In such a case, other tests (exome or genome) can be performed to dispel the doubts.

The costs of an array CGH are covered by some private insurances and sometimes depend on certain criteria (patient’s medical history, family history, abnormal findings in ultrasound scans…). You can come to us with a certificate from your doctor or with your insurance card.