Chorionic villus sampling 


The chorionic villi

At an early stage of pregnancy, the embryo divides into two parts. One part develops into the baby and the other part develops into the placenta.

The part of the embryo that forms the placenta starts out as finger-like sections called chorionic villi. These burrow into the wall of the womb to get close to the mother's blood vessels.

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Chorionic villus sampling (CVS) is a test carried out during pregnancy most commonly to check your baby for disorders such as Down’s syndrome and, where appropriate, rarer specific inherited disorders.

It involves removing and testing a sample of cells from the placenta (the organ linking the mother’s blood supply with her unborn baby’s).

CVS is offered in pregnancies where there is a high risk of the baby having such conditions. This could be because:

If there is a risk of your child being born with one of these conditions, a specialist involved in carrying out the test will be able to discuss testing with you.

In some cases, you may be referred to a genetic counsellor (a healthcare professional trained in genetics). They will discuss your risk of passing on certain genetic conditions and can offer you advice about what to do when you get the results.

Read more about why CVS is used.

How CVS is performed

CVS is usually carried out between the 11th and 14th weeks of pregnancy, although it is sometimes performed later than this if necessary.

During the test, a sample of cells, called chorionic villi cells, will be taken from the placenta using one of two methods:

  • transabdominal CVS – a needle is inserted through the abdomen (this is the most common method used)
  • transcervical CVS – a tube or forceps (smooth metal instruments that look like large tongs) are inserted through the cervix (the neck of the womb)

The test itself takes about 10 minutes, although the whole consultation will take about 30 minutes.

The CVS procedure is uncomfortable rather than painful, although you may experience some cramps that are similar to menstrual cramps for a day or two afterwards.

Read more about what happens during CVS.

Getting the results

The first results of the test should be available within two to three working days and this will tell you whether a major chromosome condition, such as Down’s syndrome or Edward’s syndrome, has been discovered.

If rarer conditions are also being tested for, it can take two to three weeks to come back. If the test is looking for a specific disorder, it can take up to a month to get the results.

If your test shows that your baby has a serious inherited or genetic disorder, the implications will be fully discussed with you. There is no cure for most of the conditions tested for using CVS, so you will need to consider your options carefully.

You may choose to continue with your pregnancy, while gathering information about the condition so you are fully prepared, or you may consider having a termination (abortion).

Read more about the results of CVS.

What are the risks of CVS?

Before you decide to have CVS, the risks and possible complications will be discussed with you.

One of the main risks associated with CVS is miscarriage, which is the loss of the pregnancy in the first 23 weeks. This is estimated to occur in 1-2% of cases.

There are also some other risks, such as infection or needing to have the procedure again because it wasn't possible to test the first sample removed.

The risk of CVS causing complications is higher if it is carried out before the 10th week of pregnancy, which is why the test is only carried out after this point.

Read more about the possible complications of CVS.

What are the alternatives?

An alternative to CVS is a test called amniocentesis. This is where a sample of the mother's amniotic fluid is removed for testing. It is usually carried out between the 15th and 18th week of pregnancy, although it can be performed later than this if necessary.

This test may have a slightly smaller risk of causing a miscarriage, but your pregnancy will be at a more advanced stage before you can get the results and consider your options.

A termination should ideally be carried out as early in the pregnancy as possible. Under UK law, an abortion can usually only be carried out during the first 24 weeks of pregnancy. However, they can lawfully be carried out after this point if tests have shown the child will most likely be born with a serious abnormality or disability.

If you are offered tests to look for a genetic disorder in your baby, a specialist involved in carrying out the test will be able to discuss the different options with you and help you and your partner make a decision.

Page last reviewed: 14/10/2013

Next review due: 14/10/2015


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The 2 comments posted are personal views. Any information they give has not been checked and may not be accurate.

rainorshine said on 30 June 2011

I found this info very useful, as I am 42 and none of the midwifes or doctors told me that the surgical termination has to be done by 12 week (after the screening (13 week) and after the Amniocentisis (15 weeks onwards) , Women need this information in order to have 'informed choices'.

What is the point of having a screening and a Amniocentisis if it is too late which leave you onlywith the choice to terminate the pregnancy with induced labour. Is this what women want? I doubt it.
I am now going to book the CVS even if I have to pay, at least I'll have a choice depending on the outcome.

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hopeful28 said on 25 September 2010

I found this extremely unhelpful, especially the beginning part which says CVS is available to women who CV are at greater risk of having a baby with an inherited disorder, such as Down’s syndrome or muscular dystrophy. This could be because:

•there is a family history of the condition
•the pregnant woman is over 35 years of age

I am 28 and don't fall into either of these categories, though after a nuchal translueceny scan I have been given a 1 in 2 chance that may baby has downs. Also the 2% rate of miscarrages after CVS is completely different to what I have read elesewhere and to what I have been told at the NHS hospital by 2 different doctors - I have been told it is between 0.5-1%

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