Chorionic villus sampling

Chorionic Villus Sampling (CVS) requires a small sample of tissue, the chorionic villi, from the developing placenta and is one of two tests available to check the chromosomes (the structures that contain genes) of your baby. This tissue may also be used for biochemical or direct genetic testing.

CVS is performed at 11 to 12 weeks in your pregnancy and is a day patient procedure.

An ultrasound will be performed first to check how far pregnant you are and to show the position of the baby and the developing placenta. As the baby is small and not fully developed, very few physical problems can be detected at this stage by ultrasound scan. Your bladder should be full but need not be uncomfortable.

CVS procedure

Chorionic villi is obtained by inserting a needle through the mother’s abdomen (which has been cleaned with antiseptic and numbed with anaesthetic) under ultrasound guidance into the developing placenta. A small sample of chorionic villi is withdrawn.

The chorionic villus sample is sent to the laboratory for testing. A chromosome result will be available in one to two weeks. A biochemical or direct genetic (DNA) test may take longer.

The chromosome test establishes the sex of the baby and if you wish to know this information you must ask the person who gives you your result.

CVS carries a small risk of causing a miscarriage. The average risk is one chance in 100. There is a risk of naturally occurring miscarriage in all pregnancies. The risk is highest in early pregnancy and increases with the age of the mother. The risks quoted for prenatal tests are in addition to this naturally occurring risk of miscarriage.

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