Chorionic villus sampling (CVS)
Chorionic villus sampling, or CVS, is an antenatal test that is used to detect genetic conditions such as Down's syndrome and some inherited disorders. CVS does not detect open neural tube defects such as spina bifida.
A small sample of cells is collected from the placenta for testing using a needle through the abdomen, or with a tube and forceps through the cervix.
CVS is likely to be offered to women thought to be at a higher risk of having a baby with birth disorders.
The reasons for the test will be discussed, as well as the risks. There is a small risk of miscarriage or infection from the CVS procedure.
What are the benefits of CVS?
CVS can be done early in pregnancy, at about 10 weeks onwards (earlier than amniocentesis, usually carried out at 15-20 weeks), and first results are usually available within a few days. Getting this kind of information early allows a woman to make choices in the early stages of her pregnancy. If a woman chooses to terminate the pregnancy after receiving abnormal test results, the pregnancy termination will be safer than if she had waited for amniocentesis results.
What are the risks of CVS?
CVS may carry a slightly higher risk of miscarriage than amniocentesis, since the procedure is done in early pregnancy. Infection may also occur. Rare cases of defects in baby's fingers or toes have been reported, especially when CVS was done before nine weeks. This risk seems unrelated to the experience of the doctor performing the test or how the test was done. Due to this potential risk, 10 weeks is generally the earliest recommended time to perform this test. Overall, the risk of miscarriage is around 1-2%.
Who should be tested with CVS?
According to the Royal College of Obstetricians and Gynaecologists, women may consider CVS if:
- They have had a previous pregnancy affected with a disorder.
- They have one or more relatives affected with a genetic disorder.
- Themselves or their partner are at greater risk of having a child with a genetic disorder, such as cystic fibrosis, thalassaemia or sickle cell disease.
- They have received a result from a scan that shows certain features, such as increased fluid at the back of the baby's neck (nuchal translucency) indicating the baby may have a disorder such as Down’s syndrome.
- They have an increased risk of a chromosomal disorder because they are over a certain age (typically 35 years).
- Want to know for certain whether the baby has a disorder.
Your obstetrician can advise you on whether this test is right for you. In the end, only you and your partner can decide whether or not you should have this test, but if there is not a specific indication and it is just because you want to know if the baby is normal, it will not be carried out on the NHS and you would have to pay. Even then an obstetrician may not agree to do the test privately if he or she feels the risks are unwarranted.