Chorion Villus Sampling (CVS) and Amniocentesis


Chorion Villus Sampling (CVS)

CVS involves the examination of chorionic villi (placental fragments). Both the baby and placenta (afterbirth) are developed from the same cell and so the chromosomes present in the cells of the placenta can be used to check the chromosomes of the baby.

  • How is CVS done?

A local anaesthetic is given. A fine needle is then passed into the uterus through the mother's abdomen and a sample of chorionic villi is taken. The needle is carefully watched with an ultrasound scan to insure it does not injure the fetus. The whole procedure takes two to three minutes to do and afterwards we check that the fetal heart is normal.

  • What should I expect after CVS?

In the first couple of days you may experience some abdominal discomfort, period-like pain or a little bleeding. 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. If there is a lot of pain or bleeding or if you develop a temperature, please contact your GP or hospital immediately.

  • When can I expect to get the result?

A preliminary result is usually available within seven days and a final result within two to three weeks. As soon as we get the result, we will call you to let you know. A report will be sent your doctor.

  • Will the procedure need to be repeated?

In approximately one per cent of cases the invasive test will need to be repeated. This is because the cells may not grow in the laboratory or the results are inconclusive.

  • What are the risks associated with the test?

The risk of miscarriage due to CVS is about one per cent and this is the same as the risk of amniocentesis at 16 weeks. Some studies have shown that when CVS is done before 10 weeks there is a small risk of abnormalities in fingers and/or toes. To avoid this risk we never performs CVS before 11 weeks.


Amniocentesis is an invasive test which involves passing a thin needle into the uterus in order to remove a small volume of fluid from around the fetus. The fluid is fetal urine and the amount lost reforms within a few days.

Amniocentesis gives the same information as CVS. However, the earliest gestation at which it can be carried out safely is 16 weeks.

Preliminary results are available within four days and a final result within two to three weeks. As soon as we get the result we will call you to let you know.

The risk of miscarriage from amniocentesis is one per cent. In less than one per cent of cases the test needs to be repeated because of inconclusive results.

  • Normal results

The majority of patients having a CVS or amniocentesis will get a normal result, their pregnancy will proceed with no problems and they will deliver a normal baby. However, a normal result does not exclude the possibility of other abnormalities and in some cases (for example those with increased nuchal translucency) we may well ask to see you again for further scans and investigations. We will keep you informed of our findings and we will discuss the various options for the subsequent management of your pregnancy.

  • Abnormal results

Unfortunately in a few cases the results of the CVS or amniocentesis will be abnormal. We will endeavour to give you as much information as you wish concerning the abnormalities. This information can be given to you over the phone but we can also arrange for you to be seen by an expert for further counselling within two to three days.

If you decide to continue with the pregnancy we will put you in touch with various support groups to improve your understanding of the condition of your baby. We may also ask to see you again for further scans to monitor your pregnancy closely and advise on the best time, method and place for your delivery.

If you choose to have a termination of pregnancy we will help make the necessary arrangements for the procedure to be carried out. We will also ensure that you have postnatal counselling.

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