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. This test is typically 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 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.

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

●A doctor or another person called a "sonographer" will do an ultrasound. This lets them see the uterus, fetus, amniotic fluid, and placenta.

●While looking at the ultrasound pictures, the doctor will usually put a needle into your belly. But sometimes, they will put a tiny tube into your vagina instead.

●They will guide the needle or tube into your placenta (figure 2). Then, they 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:

●Miscarriage (pregnancy loss)

●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.

Call your doctor if:

●You continue to have vaginal bleeding.

●You are leaking fluid from your vagina.

●You have cramps that are getting worse.

●You have a fever higher than 100.4°F (38°C).

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.

Is it better to do CVS or amniocentesis? — It depends on your individual situation. If you decide to have testing, you might choose CVS over amniocentesis because:

●You want results as early as possible in the pregnancy.

●You want results more quickly after the test.

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.)

What do my results mean? — If your results come back normal, it means that the fetus does not have the condition that 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.

More on this topic

Patient education: Amniocentesis (The Basics)

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