Chorionic Villous Sampling (CVS) is a test which samples a small piece of the developing placenta.

Chorionic Villous Sampling (CVS) is performed for chromosome and genetic analysis. The most common chromosome abnormality found is Down Syndrome (Trisomy 21). The test is ideally performed between 11-13 weeks from the first day of your last menstrual period. This will depend to some extent on, the position and thickness of the placenta.

This test is offered to pregnant women who are at an increased risk of having a child with a chromosomal or genetic abnormality.

Chorionic Villous Sampling (CVS) can also be used to diagnose several rare hereditary metabolic diseases. However, the laboratory procedures are very specific and are only performed if you are at high risk of having a baby with this problem, after having been investigated by a Clinical Geneticist. Tests of this kind need to be arranged well before the date of CVS, as special laboratory preparation is often required. The test does not prove the baby is normal. In every pregnancy there is a small but definite risk that the baby may have an abnormality. Chromosome abnormalities account for only 5% of these abnormalities. Therefore, a normal result of the test cannot rule out other problems (e.g. heart defects, cerebral palsy, autism, cystic fibrosis, club foot or cleft lip etc.)

Before your scan

If possible, please wear comfortable, loose-fitting clothing that allows easy access to the area that is being imaged. Two-piece clothing is ideal (separate upper/lower garments).

Please empty your bladder 2 hours before the examination time. Then slowly drink 600ml of water to fill your bladder and keep it full for your examination.

Arrange to have someone care for any young children for the whole day of your test.


When you visit Adelaide Women’s Imaging for a CVS, you will be greeted by one of our friendly reception staff who will check we have all the necessary paperwork including your blood group. A sonographer will then collect you from the waiting room and take you to the ultrasound room. One of our doctors will speak with you prior to the procedure and this is an opportunity for you to ask additional questions. The procedure is performed by an Adelaide Women’s Imaging obstetrician and gynaecologist in one of our ultrasound rooms.

Firstly, an abdominal ultrasound is performed to find the position of the placenta. The skin is then cleaned with a disinfectant, and local anaesthetic is injected under the skin. A needle is guided under ultrasound control through the abdominal wall into the placenta, and a small amount of tissue is drawn through the needle. The actual test itself takes only 5-10 minutes; the preparation takes longer.

Once the procedure is completed the sample is sent off for laboratory tests. The results of the chromosome are usually known within 10-14 days. A comprehensive report of the procedure and the final laboratory tests will be sent directly to your referring GP or specialist.

After your procedure

On the day of the test, do not overexert yourself. A day off from work is recommended, no sport, intense exercise etc. Let your body guide you; if your abdomen is still tender or uncomfortable the following day, then continue to take things easy.

Some cramping abdominal pain, similar to period pain, can be expected. Rarely a small amount of bleeding may occur. The bleeding should not be heavier than a period and the abdominal discomfort usually settles within an hour or two.

Should you be concerned about your symptoms, please phone the clinic on 8193 9522 or contact your Obstetrician or General Practitioner.

Frequently Asked Questions – Chorionic Villous Sampling (CVS)

Does CVS tell me if my baby had spina bifida?

No. The gold standard for diagnosing spina bifida is a detailed ultrasound at 19+ weeks that can detect up to 95% of babies with this problem.

What must I do and not do after the test?

On the day of the test, do not overexert yourself. A day off from work is recommended, no sport, intense exercise etc. Let your body guide you; if your abdomen is still tender or uncomfortable the following day, then continue to take things easy.

Does this test assure me that my baby will be normal?

No. A CVS can only tell you if the baby’s chromosomes are normal or if he/she is affected by the inherited disease for which he/she is specifically tested. Unfortunately, a normal CVS result does not assure you of a normal baby.

How reliable are the results?

In about 1% of cases different colonies of cells are found in the placenta. This is known as mosaicism and can make the CVS result difficult to interpret. In these cases you will be advised to have an amniocentesis at greater than 15 weeks.

Other results (e.g. cystic fibrosis, muscular dystrophy placenta etc.): The clinical geneticist who advised you prior to the CVS will have told you how accurate the results of the test will be in your case. These tests are only performed in patients with a known increased risk.

I had an amniocentesis in my last pregnancy, but am wondering whether to do the same this time or try a CVS? What are the pros and cons of each?

Unless your doctor has informed you otherwise, the choice between the two tests is purely personal and rests with you and your partner.

I have a twin pregnancy and was planning to have a test to exclude Down Syndrome. Can I have a CVS?

Yes, a CVS may be able to be performed. It is very important to have fully discussed the implications of an abnormal result in one or other of the babies.

I know the maximum risk of miscarriage is about 1%, but when can I relax knowing the risk is behind me?

The risk of having a miscarriage for anyone who has reached 10 weeks of pregnancy is 2-3% even without a CVS. The risk of a spontaneous miscarriage decreases after 13 weeks. The additional risk caused by the CVS has probably largely passed once any symptoms have gone. Once you have passed 13 weeks, the risk of miscarriage for any reason is minimal.

If I choose to have a CVS rather than an amniocentesis, will it always be done?

If a CVS will give you the results you require, then we will attempt to perform this test. However, sometimes it is technically not possible to obtain the Chorionic Villous tissue we require (due to the position of the placenta or to fibroids etc). If waiting a week or so is unlikely to improve our chances, then you would be advised to have an amniocentesis. We also may not perform a CVS if there has been (bright) vaginal bleeding in the week prior to the test.

My blood group is Rhesus negative. Do I need an injection of anti-D after the test?

Generally, yes. Anti-D (or an equivalent) is usually given to all Rh-negative women after this test.

What are the risks of a CVS?

CVS is associated with a risk of miscarriage in the order of around 1%.

Are you ready to make your Chorionic Villous Sampling (CVS) appointment?