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Prenatal Genetic Testing

What is prenatal genetic testing?

This type of testing, also known as prenatal diagnosis (PND), is performed during pregnancy to determine whether or not the foetus is affected by or at risk of being affected by a genetic condition.

Prenatal testing would be offered to parents when there is an increased risk of having a child with a specific genetic condition. For example, if both parents are carriers of Tay Sachs disease, prenatal testing could determine whether the baby would be affected by the disorder.

What does prenatal testing involve?

There are currently two main types of prenatal tests available:

  • Chorionic villus sampling (CVS) involves removal and testing of cells from the early placenta (chorion) surrounding a developing foetus. It is performed at around the 12th week of pregnancy and results tend to take 1 to 2 weeks to process.
  • Amniocentesis involves removing and testing of cells from the amniotic fluid that surrounds the developing foetus. It is performed from around the 15th week of pregnancy and results usually take up to 2 weeks to process, although for certain tests results can take longer.

The two tests differ in timing, process and risk of miscarriage, however, the genetic testing procedure on the extracted sample cells tends to be the same for both. 

Things to consider prior to having prenatal testing

Prenatal testing does have an associated risk of miscarriage which differs depending on the procedure used and is worth discussing with your doctor or genetic counsellor prior to testing.

Establishing a diagnosis in pregnancy gives parents the opportunity to choose whether or not to continue the pregnancy. Parents who know they would not have a termination may still opt for prenatal testing in order to prepare themselves for having a child with a genetic disorder.

If the results of the prenatal tests find that the genetic disorder has been passed on, further information and support are available to you from your genetic counsellor and also from an organisation called ARC (Antenatal results and choices).