Patient education: Chorionic villus sampling (The Basics)

What is chorionic villus sampling? — 

Chorionic villus sampling, or "CVS," is a test that is performed on the placenta. The placenta is the organ inside a pregnant person's uterus that brings the fetus nutrients and oxygen, and carries away waste (figure 1). The fetus (developing baby) and its placenta almost always share 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.

CVS can be done in 2 ways (figure 2). The doctor can access the placenta through the:

●Belly – This is called a "transabdominal CVS." The doctor inserts a needle through the skin of the belly and into the uterus to get a sample of the placenta.

●Cervix – This is called a "transcervical CVS." The doctor inserts a small tube through the vagina and cervix to get a sample of the placenta.

The doctor will decide which way to do the procedure based on the position of your uterus and placenta.

Why is CVS done? — 

CVS is done to check if your fetus has a specific genetic problem like Down syndrome, Tay-Sachs disease, cystic fibrosis, or another disease. You might choose to have this test if someone in your family had one of these conditions. Or you might have it if another test suggests that your fetus has a specific genetic problem. CVS cannot check for every possible genetic problem.

When is CVS done? — 

CVS is typically done between 10 and 13 weeks of pregnancy.

Is there an alternative to CVS? — 

There is another test called "amniocentesis" that can also check for genetic problems in the fetus. But amniocentesis is done later in pregnancy, usually around week 16.

The choice of which test to have depends on your situation. If you decide to have testing, you might choose CVS over amniocentesis because you want results as early as possible in the pregnancy.

Amniocentesis will probably be done instead of CVS if you are already in your second trimester. (This means that you have been pregnant for more than 3 months.)

How is CVS done? — 

When it is time for the procedure:

●A doctor or another person called a "sonographer" will do an ultrasound. This lets them see the uterus, fetus, amniotic fluid, and placenta. The doctor will look at the ultrasound pictures as they do the procedure.

•For a transabdominal CVS – The doctor will clean your belly and might numb the skin where they are going to insert the needle. You might feel some pressure or discomfort as the doctor inserts the needle through your belly and uterus into your placenta.

•For a transcervical CVS – The doctor will use a device called a "speculum" to keep your vagina open and let them see your cervix. They will also use a device to hold your cervix in place. They will place a small tube through your vagina and cervix to get to your placenta.

●They will guide the needle or tube into your placenta (figure 2). Then, they will take a very tiny sample of tissue. If you are pregnant with more than 1 baby (for example, twins), the doctor might need to take more than 1 sample.

●The tissue will be sent to a lab for tests.

What are the risks of CVS? — 

Your doctor will talk to you about all of the possible risks, and answer your questions. Problems are rare, but they can happen. Risks include:

●Pregnancy loss (miscarriage)

●Infection

●Leaking of blood from the fetus into your own bloodstream – If you have "type negative" blood and this happens, it can cause problems for later pregnancies. Your doctor can give you a shot of medicine to prevent these problems.

What happens after CVS? — 

You might have a small amount of bleeding or "spotting" from your vagina for a short time. Your doctor or nurse might tell you to avoid heavy exercise and sex for 24 hours. But otherwise, you can go back to your usual activities.

What do my results mean? — 

Results of CVS usually come back in a few days. If your results come back normal, it means that the fetus does not have the condition the doctors tested for. But CVS cannot check for all genetic problems.

Your doctor or genetic counselor can help you understand what your results mean. They can also help you decide if any other steps are needed.

When should I call the doctor? — 

Call your doctor or nurse if you:

●Continue to have vaginal bleeding

●Are leaking fluid from your vagina

●Have cramps that are getting worse

●Have a fever higher than 100.4°F (38°C)

More on this topic

Patient education: Amniocentesis (The Basics)

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