Chorionic villus sampling (CVS)
Chorionic villus sampling (CVS), is an antenatal test that is used to detect genetic conditions. These include:
CVS does not detect open neural tube defects such as spina bifida.
A small sample of cells is collected from placental tissue (called chorionic villi) for testing using a needle through the abdomen, or with a tube and forceps through the cervix. The placenta is the organ that provides nourishment to a growing baby in the womb during pregnancy.
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.
Some women will decide to terminate a pregnancy after receiving abnormal test results. In these cases, the termination will be safer because it is done earlier than waiting for amniocentesis results.
What are the risks of CVS?
Because CVS is done earlier in pregnancy, there may be a slightly higher chance of having a miscarriage than with amniocentesis. The NHS puts the miscarriage risk at up to 1 in 50.
There is also a risk of infections from the procedure.
Who should be tested with CVS?
The test is voluntary and may be offered if a woman:
- Has had earlier antenatal tests suggesting genetic problems
- Has had a previous pregnancy involving a genetic disorder
- Has a family history of genetic conditions, including cystic fibrosis or muscular dystrophy, and an abnormality is suggested by routine ultrasound scans
A doctor or midwife will explain the reasons for offering the test, how it is done - and the risks - such as miscarriage.
Some women may prefer to wait until later in the pregnancy to find out if the baby is likely to have a genetic problem.
How is the CVS test carried out?
No special preparations are needed on the day of the test unless you are told otherwise. Because it can be a very emotional time - it helps to take a partner, family member or friend along with you for support.
You may be asked to avoid having a wee for some time before the test as it is easier to do it when the bladder is full.
There are two ways to collect the cell samples - through the vagina or through the abdomen.