Chorionic Villus Sampling

Chorionic Villus Sampling (CVS) is used as a diagnostic test when there is a high risk the baby may have a chromosomal anomaly such as Down's Syndrome. It involves taking a tiny sample of placental tissue, which originates from the same cells as the baby.

The procedure is done by passing a fine needle through the mother’s abdomen and into the placenta, whilst continuously monitoring the baby and the needle using the ultrasound scan. Local anaesthetic is initially given to reduce the discomfort. The whole procedure lasts approximately 1 minute and the baby’s heartbeat is checked afterwards.

There may be some abdominal discomfort or a little bleeding for the first day or so after the procedure. These are relatively common and in the vast majority of cases the pregnancy continues without any problems. You may find it helpful to take simple painkillers like paracetamol.

However, the procedure has a risk of miscarriage of 0.5%. Therefore, if there is a lot of pain or bleeding or if you develop a temperature please seek medical advice.

The results of the CVS for Down's Syndrome and the other common major chromosomal defects are usually available within 3 working days. A full result of all the chromosomal anomalies including the more rare anomalies would be available 2 weeks after the procedure.

Very rarely (1:300), the 3-day test fails and you will need to wait for the 2 weeks to get a result. Also in 1:250 cases the CVS results are inconclusive and an amniocentesis may be recommended.