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 a fetus using a sample taken from the placenta. The placenta usually has the same genes as the fetus. The placenta is a large organ that forms in your uterus when you are pregnant. It supplies the fetus with nutrients and oxygen through the umbilical cord. A small piece of the placenta is taken out and tested.

This test is done when you are 10 to 13 weeks pregnant.

Why is this test done?

CVS can find certain genetic conditions. It can also find chromosome problems, such as Down syndrome.

You may want to have this test because:

• You are concerned about the fetus because of your age. As you get older, you have a greater chance of the fetus having a genetic condition.
• You've had a baby with a genetic condition.
• You or the father has a family history of a genetic condition.
• You had a screening test with a result that was not normal.

How do you prepare for the test?

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

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

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).

Through the belly

• You will lie on your back on an exam table.
• Your belly will be cleaned with an antiseptic.
• Your doctor will use ultrasound 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 exam table.
• Your doctor will put a tool with curved sides (speculum) into your vagina.
• Your doctor will use ultrasound to guide a thin tube (catheter) through your cervix to the placenta.

What are the risks of the test?

Some risks of CVS may include:

• Infection in your uterus.
• Vaginal bleeding.
• Leakage of amniotic fluid.
• Miscarriage. The risk of miscarriage is very low. A miscarriage may happen in about 2 out of 1,000 cases.
• A false-positive result. In rare cases, this can happen when the placenta cells have abnormal genetic material even though the fetus's cells are normal. This is called confined placental mosaicism.

There is a very small chance that CVS could cause bleeding that could let your blood mix with the fetus's blood. If you have Rh-negative blood, you will be given the Rh immunoglobulin shot (such as RhoGAM). This can prevent Rh sensitization, which could cause harm if the fetus has Rh-positive blood.

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 needle for collecting the sample is put in the belly. You may have some cramping when the needle is in your uterus.

Through the cervix (transcervical)

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?

Contact your doctor or midwife now or seek immediate medical care if:

• You have cramping that doesn't go away.
• You have vaginal bleeding that doesn't go away.
• 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 or midwife 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 contact your doctor 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.