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Patient education: Chorionic villus sampling (The Basics)
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Patient education: Chorionic villus sampling (The Basics)
Written by the doctors and editors at UpToDate
All topics are updated as new evidence becomes available and our peer review process is complete.
Literature review current through: Oct 2017. | This topic last updated: Feb 15, 2017.

What is chorionic villus sampling? — Chorionic villus sampling, also called CVS, is a test that takes out a tiny piece of the placenta. The placenta is the organ inside a pregnant woman's uterus that brings her fetus nutrients and oxygen, and carries away waste (figure 1). The fetus and its placenta share many of the same genes.

CVS can show if there is something wrong with the fetus's genes or chromosomes. Chromosomes are structures within cells that contain thousands of genes. This test is done between 10 and 13 weeks of pregnancy. Results come back in a few days.

Why is CVS done? — CVS is done to check if your fetus has a specific genetic problem, such as Down syndrome, Tay-Sachs disease, cystic fibrosis, or another disease. You might have this test if you have a family history of one of these conditions, or if another test suggests your fetus has a specific genetic problem. Keep in mind, though, that doctors cannot use CVS to check for every possible genetic problem. If your CVS results come back normal, that does not necessarily mean the fetus has no genetic problems. It just means it does not have the condition the doctors tested for.

How is CVS done? — Here are the main steps:

The doctor will do an ultrasound. That is an imaging test that uses sound waves to create a picture of your uterus, fetus, and placenta.

While looking at the ultrasound picture, the doctor will put either a needle into your belly or a tiny tube into your vagina (figure 2).

Next, the doctor will guide the needle or tube into your placenta. Then, he or she will take a very tiny sample of tissue.

The tissue will be sent to a lab for tests.

Does CVS have any risks? — Yes. Problems are rare, but they can happen. Risks include:


Leaking of blood from the fetus into your own bloodstream. This can cause problems for later pregnancies.

Should I be worried about symptoms after the procedure? — That depends on what symptoms you have and how bad they are. After CVS, it is normal to bleed a little from your vagina.

Call your doctor if:

You have vaginal bleeding that is like what you have during your period

You are leaking fluid from your vagina

You have cramps that are getting worse

You have a fever higher than 100.4°F (38ºC)

Is there an alternative to CVS? — There is another test, called amniocentesis, which can also test for genetic problems in the fetus. But amniocentesis is done later in pregnancy, usually around week 15 to 17.

Is it better to do CVS or amniocentesis? — That depends on your individual situation. You might not need either one. If you do decide to have testing, you might choose CVS over amniocentesis because:

You want results as soon as possible in the pregnancy

You want results more quickly after the test

You might choose amniocentesis over CVS because:

There is slightly less risk of miscarriage with amniocentesis

You are already in the second trimester, meaning you have been pregnant for more than 3 months

What if the test shows my fetus has a specific genetic problem? — You should talk to a genetic counselor before and after the test. He or she can help you understand what to expect, your feelings, and what to do.

More on this topic

Patient education: Amniocentesis (The Basics)

Patient education: Chorionic villus sampling (Beyond the Basics)
Patient education: Amniocentesis (Beyond the Basics)

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Topic 15612 Version 4.0

All topics are updated as new information becomes available. Our peer review process typically takes one to six weeks depending on the issue.