Chronic Villous Sampling (CVS)

On the day

When you visit Adelaide Women’s Imaging for a CVS you will be greeted by one of our friendly reception staff who will show you to the ultrasound room. You may need to change into a medical gown for your procedure.

The procedure is performed by an Adelaide Women's Imaging obstetrician and gynaecologist.

Once the procedure is completed the sample is sent off for laboratory tests. The results of the chromosomes are usually known within 7-10 days. Once we receive the results one of our qualified obstetricians / gynaecologists will prepare a comprehensive report for your referring GP or specialist.


Does this test also tell me if my baby has spina bifida?

No. A blood test at 16 weeks and/or a detailed ultrasound at 19+ weeks can detect up to 95% of babies with this problem.

What must I do / not do after the test?

On the day of the test, do not over exert yourself (take it easy, a day off work is suggested), 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.

What will happen if the results of my CVS are not good (for isntance if the test shows that my baby has Down syndrome?).

This should be discussed before the test is done. Your doctor will inform you of the results. You must then decide what you will do with the information. The options available are either to continue with the pregnancy or to terminate the pregnancy. Should you decide to continue the pregnancy, you will then have time to prepare and inform yourself of the potential problems you and your child are likely to face. Should you decide not to proceed with the pregnancy, a procedure can usually be performed. You will need to discuss these aspects with your obstetrician.

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?

Chromosome results: the result from the placenta is the same as the baby in 99 out of 100 tests. In the other 1 %, the placenta has different chromosomes to those of the baby. 1:300 cases have a mixed result. If this is the case you will be advised to have an amniocentesis at 16 weeks of pregnancy to confirm the baby’s chromosomes. Other results (i.e. for 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 test?

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. This will need to be discussed, in detail, ideally well before 11 weeks.

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 fairly minimal.

If I choose to have 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 impossible to obtain the chorionic villous tissue we require (due 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?

Miscarriage: Approximately one in a hundred women will have a miscarriage as a result of the procedure.

CVS is a test which samples a small piece of the developing placenta (after-birth).

The test is performed for chromosome analysis. It looks for abnormalities in the number or form of the chromosomes of the baby and placenta. The most common chromosome abnormality found is Down syndrome (Trisomy 21). Other inherited diseases which can be in certain cases diagnosed from placental tissue include cystic fibrosis, muscular dystrophy, thalassemia, fragile X, etc.

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.

Who is offered this test?

Pregnant women at increased risk of having a child with a birth defect which could be detected by using this test.


Arrange to have someone care for any young children for the whole day of your test. Please empty your bladder two hours before the appointment time, and then drink 600ml of water to fill your bladder and keep it full for your examination.


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 into a syringe. The actual test itself takes only 5-10 minutes; the preparation takes longer.

After your procedure

Some cramping abdominal pain (like 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 a day or two.

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