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Chorionic Villus Sampling (CVS): About This Test

What is it?

Chorionic villus sampling (CVS) is a test done during pregnancy. It looks for certain genetic problems with your baby (fetus). The same genes that are in your baby are in the placenta. The placenta is a large organ that forms in your uterus when you are pregnant. It supplies your baby with nutrients and oxygen through the umbilical cord. A small piece of the placenta is taken out and tested.

This test is usually done when you are 10 to 13 weeks pregnant but it can be done later in your pregnancy if needed.

Why is this test done?

CVS can find genetic conditions, such as Tay-Sachs disease or hemophilia. It can also find chromosomal abnormalities, such as Down syndrome (Trisomy 21), Trisomy 13, and Trisomy 18.

You may want to have this test because:

  • Your age may be a concern. As you get older, you have a greater chance of having a baby with a chromosomal abnormality that may have birth defects.
  • You have had a baby with a birth defect.
  • You or your partner has an ethnic background in which inherited diseases are common.
  • You or your partner has a family history of an inherited form of intellectual disability. Or either of you has a known genetic condition.
  • You had a result from a screening test (a blood test or ultrasound) that was not normal.

How do you prepare for the test?

You may want to talk to a genetic counsellor before or after the test. This person is trained to give you detailed information about the test. They can help you make decisions about testing. The counsellor can also help you understand the results of the tests.

You may be asked to drink a glass of fluid about an hour before the test so that your bladder is moderately full. A moderately full bladder makes it easier to do the test.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

How is the test done?

There are two ways to do this test. One way is through the belly (transabdominal). The other way is through the cervix (transcervical).

  • You will lie on your back on an examination table.
  • Your belly will be cleaned with an antiseptic liquid.
  • Your doctor will use ultrasound with sterile gel to guide a long, thin needle through your belly and uterus to the placenta. The needle is used to collect a sample of the chorionic villus cells.

Through the cervix

  • You will lie on your back on an examination table.
  • Your doctor will put a tool with curved sides (speculum) into your vagina, like a pap test.
  • Your doctor will use ultrasound with sterile gel to guide a thin tube (catheter) through your cervix to the placenta.

How does having chorionic villus sampling (CVS) feel?

Through the belly (transabdominal)

You may feel a short, sharp sting from the needle used to give the numbing medicine. There is usually no pain when the collecting needle is put in the belly. You may have some cramping when the needle is in your uterus.

Through the cervix (transcervical)

Most women do not find this procedure painful. You may feel some pressure or mild discomfort when the speculum is placed in your vagina. You may have some cramping when the catheter is put through your cervix.

How long does the test take?

The test will take about 30 minutes. Getting the sample takes only a few minutes.

What happens after the test?

  • You will probably be able to go home 15 to 30 minutes after the test.
  • Your doctor may ask you to avoid strenuous exercise, lifting anything heavy, and sex after the test. By the next day, you can do your normal activities, unless your doctor tells you not to.
  • You may have some cramping or vaginal spotting. This should go away within a day. You may feel some soreness where the needle was put in if you had the belly procedure done.

When should you call for help?

Call your doctor, midwife, or nurse advice line now or seek immediate medical care if:

  • You have cramping.
  • You have vaginal bleeding.
  • You have pain in your belly or pelvis.
  • You notice fluid coming from your vagina.
  • You have a fever.

Watch closely for changes in your health, and be sure to contact your doctor, midwife, or nurse advice line if you have any problems.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse advice line (811 in most provinces and territories) if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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