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

CVS is performed at 11 to 12 weeks in the 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 can be 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 A small sample of chorionic villi is withdrawn.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 chorion 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.

CVS carries a small risk of causing a miscarriage. The average risk is one chance in 100.

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.