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Chorionic villus sampling

Published by Bupa's health information team, September 2008.

This factsheet is for women who are considering having chorionic villus sampling (CVS), or who would like information about it.

CVS is a test carried out during pregnancy to detect specific abnormalities in a developing baby (fetus).

Your care will be adapted to meet your individual needs and may differ from what is described here. So it's important that you follow your surgeon's advice.

About chorionic villus sampling
What are the alternatives?
Preparing for your chorionic villus sampling
About the procedure
What to expect afterwards
Recovering from chorionic villus sampling
What are the risks?
Further information
Questions and answers
Related topics
Sources

About chorionic villus sampling

This procedure involves removing a small sample of the placenta from your womb (uterus) for testing in a laboratory. The placenta provides oxygen and nourishment to your growing baby.

The placenta has the same genetic make up as your baby so it can provide information about his or her health.

Why have chorionic villus sampling?

CVS can detect certain chromosome disorders in the baby including:

Down's syndrome (an extra chromosome 21)
Edward's syndrome (an extra chromosome 18)
some genetic (inherited) disorders (eg sickle cell anaemia, cystic fibrosis or thalassaemia)

CVS can't diagnose structural problems such as spina bifida.

When is chorionic villus sampling offered?

CVS is usually offered:

if a screening test has suggested an increased chance of Down's syndrome
for women over 35 who missed the initial screening test, as the risk of the baby having a genetic disorder increases after this age
for women who have a history in their family of babies being born with certain conditions, such as Down's syndrome
if there is a possibility of a genetic disorder, for example women who have, or whose partner has, an inherited condition
if you, your partner, or both of you are carriers of a gender-specific disease such as haemophilia or Duchenne muscular dystrophy (both of these are more likely to occur in boys)

When is chorionic villus sampling performed?

CVS is usually done between 11 and 13 weeks of pregnancy.

What are the alternatives?

Amniocentesis is another test that can diagnose problems with the baby. It tests for similar conditions as CVS.

Amniocentesis carries a lower risk of miscarriage than CVS - around one out of every 100 women.

Amniocentesis is done later than CVS, usually after 15 weeks of pregnancy. This can make a decision to end the pregnancy more difficult. When a pregnancy is ended before 15 weeks, a small operation is usually carried out. Later on, ending the pregnancy may mean going into labour.

The decisions around whether to have tests in pregnancy and what to do with the results may be difficult. It's a good idea for you to discuss the issues with health professionals before deciding to have CVS or amniocentesis.

Preparing for your chorionic villus sampling

Your surgeon will explain how to prepare for your test. It is usually done as a day case. This means you will have the test and go home the same day.

Your surgeon will usually visit you to discuss the test and ask you to sign a consent form. This confirms that you understand the risks, benefits and possible alternatives to the procedure and have given your permission for it to go ahead.

About the procedure

There are two ways of doing CVS: through the cervix (transcervical) and through the abdomen (tummy) (transabdominal).

Through the cervix

Your surgeon will use a speculum (a device that is inserted into your vagina to view the cervix) to open your vagina, and will clean the vagina and cervix.

He or she will move an ultrasound device over your abdomen to create an image of your womb on a monitor. This allows your baby's position and the position of the placenta to be seen as clearly as possible.

Watching this image, your surgeon will guide a fine tube or forceps through your cervix to the placenta. A sample is taken and the tube or forceps are removed. He or she will then check your baby again with the ultrasound.

Through the abdomen

As with CVS performed through the cervix, your surgeon will move an ultrasound device over your abdomen to create an image of your womb on a monitor.

Watching this image, he or she will guide a long, thin, needle through the wall of your abdomen and towards the placenta. This can be slightly uncomfortable so you may choose to have a local anaesthetic to numb the skin where the needle will be inserted. A sample is taken and the needle is removed. Your surgeon will then check your baby again with the ultrasound.

What to expect afterwards

Certain conditions (eg Down's syndrome and Edward's syndrome) can be identified after three working days. For an analysis of other conditions, it can take two to three weeks. This is an anxious time for everyone involved and it's a good idea to keep occupied until the results come through.

For most women the test will give a very clear result - that the chromosomes are normal or not, or for other conditions, positive or not. Occasionally a condition is detected that is different to the one originally looked for. Rarely your baby may still be born with a disorder when you have a normal result. A normal result does not exclude every disorder.

If your test gives an uncertain result, your surgeon may recommend further testing.

Before deciding to have CVS it's worth thinking about what the results will mean to you.

If the results show that your baby has normal chromosomes, this is reassuring. However, CVS can't test for every disease or guarantee that your baby will be born completely healthy.

If the CVS results are abnormal, you will need to make some informed decisions. These decisions should be based on the results of the CVS and what they mean for you, your family and your unborn baby. There are a number of options to consider.

Whether to continue with or terminate the pregnancy. If the baby has a severe defect, some women opt to end the pregnancy (therapeutic abortion). Others want time to prepare themselves and their family for the birth of a baby with health problems.
Where to have the baby. For example, if the baby has a problem that may need surgery, it would be best to give birth at a hospital where surgeons are experienced in surgery for newborns.

These decisions may be difficult and it's a good idea for you to discuss the issues with your partner, your family, your doctor and other health professionals before deciding to have CVS.

Recovering from chorionic villus sampling

If you need them, you can take over-the-counter painkillers such as paracetamol or ibuprofen. Follow the instructions in the patient information leaflet that comes with the medicine and ask your pharmacist for advice.

What are the risks?

CVS is commonly performed and generally safe. For most women, the benefits of a clear diagnosis of any problem with their baby are greater than the potential risks. However, in order to make an informed decision and give your consent, you need to be aware of the possible side-effects and the risk of complications of this procedure.

Side-effects

These are the unwanted, but mostly temporary effects of a successful treatment.

You may have some mild pain or cramps, like period pain, and spotting (light bleeding from the vagina) for a few hours afterwards. If you have any other symptoms such as feeling unwell, heavy bleeding or contractions you should see your doctor immediately.

Complications

This is when problems occur during or after the test. Most women are not affected but the risks of CVS include those listed below.

Injury to you or your baby from the needle - using ultrasound reduces this risk.
You may develop an infection because the procedure has let bacteria into the amniotic sac, but this is very rare.
There is a slight risk that your blood will be exposed to your baby's blood. This is only a problem if your blood is rhesus-negative and your baby's is rhesus positive. This risk is reduced when you are given an injection of the appropriate antibodies after your test.

Injury or infection can lead to miscarriage but this is rare, miscarriage occurs in about two in 100 CVS tests. It's thought that the risk of miscarriage might be higher with CVS performed through the cervix than through the abdomen, although more research is needed to confirm this.

The exact risks are specific to you and will differ for every person. Ask your surgeon to explain how these risks apply to you.

Further information

Royal College of Obstetricians and Gynaecologists
020 7772 6200
www.rcog.org.uk
Midwives Information and Resource Service
0800 581 009
www.midirs.org