Chorionic Villus Sampling

Details

Published on Wednesday, 05 October 2011 20:31

Written by Ginny

Chorionic villus sampling (CVS)

This is usually performed between 11 and 13 weeks of pregnancy. It is a test that involves taking a small sample of tissue from the developing placenta. This tissue is called the chorionic villi.

The placenta can be tested for chromosomal or DNA abnormalities like Down syndrome.

How is it performed? 

The skin of the lower abdomen is cleaned with and alcohol based antiseptic solution. A local anaesthetic is then injected.

 Guided by an ultrasound a fine needle is guided into the placenta and a sample is taken (the chorionic villi). A dragging sensation may be felt in the legs or pelvis during the test and this is normal.

How do I prepare? 

Your bladder is required to be moderately full. This is so the uterus is lifted out of the pelvis and easily accessible for the needle. An ultrasound will be performed before the test to ensure that your baby is alive and well, look for any abnormalities in the baby and to locate the placenta.

What happens after the test is completed? 

The specimen will be sent to a laboratory and processed. It is put in a culture and then an incubator for a few days. After the specimen has divided into enough cells it will be removed and then injected with an enzyme. The chromosomes will then be counted and analysed.

Each of the 23 pairs of chromosomes are stained with a dye and then examined under an ultra violet light. The test will not only exclude Down syndrome but also a variety of other small and major chromosome abnormalities.

After the test you should avoid any strenuous activity for the rest of the day. You may experience some mild cramps after the test. Some vaginal spotting may also be experienced.

When will  the results be available?

Generally the results take 11 -14 days, although a preliminary result is available in about 24 hours. This is known as a Flourescent in situ hybridisation (FISH) test. The FISH test can identify about 90% of the common chromosome ploblems such asthe ones involving 13, 18, 21,  X or Y. The longer result has an error rate of approximately 1 in 12,000.

What is the risk to my baby?

The risk of miscarriage is about 1 in 200.