Chorionic Villus Sampling for Prenatal Diagnosis

What is a chorionic villus sampling (CVS) test?

Chorionic villus sampling (CVS) is a type of prenatal test that can be used to diagnose the reason for some birth defects (congenital disorders) or genetic conditions in a fetus. Your pregnancy care provider may offer you CVS if you’re at high risk for having a baby with a genetic health condition. CVS testing is optional — only you can decide to have the test after discussing the risks and benefits with your provider. Healthcare providers recommend CVS testing between weeks 10 and 13 of pregnancy. It can also tell you the sex of the fetus.

CVS testing takes a small sample of cells called chorionic villi from the placenta. Chorionic villi form from the fertilized egg, so they usually have the same genetic makeup as the fetus. Your provider sends the cells to a lab for analysis.

What are reasons for having CVS during pregnancy?

CVS testing isn’t a standard part of your prenatal care. Your healthcare provider only offers it if you have certain risk factors or if they detect abnormalities on noninvasive prenatal screening or pregnancy ultrasound. But you can also choose to skip the test. It’s up to you.

Providers may offer CVS testing if you:

• Already have a child with a genetic condition.
• Are 35 or older on your due date.
• Had a previous screening or test that indicated a higher risk of having a child with a genetic condition.
• Have a personal or family history of a genetic disorder (or if your partner does).

Your provider may recommend that you skip this testing if you:

• Have had vaginal bleeding during your pregnancy.
• Have an infection, such as an STI.

What conditions does chorionic villus sampling test for?

CVS can help identify certain genetic diseases, including problems with chromosomes. Chromosomes contain the DNA and genetic makeup of a fetus. CVS can detect if there are extra or missing chromosomes (including missing parts) or if any chromosomes have significant changes to their structures. These types of chromosomal changes can lead to congenital disorders and other health problems.

Conditions CVS tests for include:

• Down syndrome (or trisomy 21).
• Cystic fibrosis.
• Sickle cell disease.
• Tay-Sachs disease.
• Trisomy 18 (or Edward syndrome).
• Trisomy 13 (or Patau Syndrome).

Does CVS testing detect all birth defects?

CVS doesn’t detect certain birth defects like neural tube defects (NTDs), which affect a fetus’s spine or brain. Spina bifida is an example of a neural tube defect. Different tests, such as an alpha-fetoprotein (AFP) test or amniocentesis can screen for NTDs.

CVS also can’t detect structural birth defects such as heart conditions or cleft lip or palate. An ultrasound when you’re around 18 to 20 weeks pregnant checks for these and other congenital disorders.

What happens before CVS testing?

Before the test, you have genetic counseling with either a certified genetic counselor or maternal-fetal medicine specialist. A genetic counselor discusses the risks and benefits of the procedure with you. You also have an ultrasound to confirm how many weeks pregnant you are. This helps your provider determine the right time to schedule CVS testing.

How does CVS testing work?

Chorionic villus sampling isn’t painful, though you may feel some discomfort. There are two ways healthcare providers perform the test:

• Transcervical (through your vagina): Your provider inserts a speculum into your vagina. This smooth device is shaped like a duck’s bill and is also used for Pap tests. It allows your provider to widen your vaginal walls. Your provider then inserts a thin, plastic tube into your cervix. Using ultrasound as a guide, your provider moves the tube to the placenta and removes a small sample of villi.
• Transabdominal (through your abdomen or belly): Using ultrasound as a guide, your provider inserts a thin needle through the skin of your abdomen to the placenta to remove the cells. If your provider uses the abdominal method, you may get local anesthesia to reduce any discomfort.

Both methods take less than 30 minutes from beginning to end.

What happens after a CVS test?

You can go home shortly after your provider finishes CVS testing. You may want to rest for several hours afterward. Most people can resume their normal activities the next day. Your healthcare provider may tell you to avoid sex, exercise or other strenuous activities for 48 to 72 hours.

Will I need more than one CVS test?

There may be reasons you need a second CVS test. In rare cases, the provider may not have collected enough cells during the procedure. You may need a second one to get enough placental cells.

Additionally, if you’re expecting twins and each fetus has its own placenta, you may need two CVS tests, one for each fetus.

What are the risks and side effects of CVS testing?

You may feel some cramping after the test. Some light vaginal spotting is normal. If your provider uses a transabdominal approach, you may also feel some soreness in your belly.

CVS testing is safe, but comes with some risks. You should discuss the risks with your healthcare provider and make sure you understand them. Some risks are:

• Miscarriage: The miscarriage risk with CVS is less than 1 in 100 or 1%.
• Infection: As with most medical procedures, there’s a small risk of infection.
• Limb deformity: Rarely, CVS testing can cause a baby to be born with a limb deformity (especially when CVS is done before 10 weeks).
• Bleeding: Light bleeding is normal, but there’s a small risk of heavy vaginal bleeding after CVS.
• Leaking amniotic fluid: You may leak too much amniotic fluid, which can cause pregnancy complications.
• Rh sensitization: This is when the pregnant person has Rh-negative blood and the fetus has Rh-positive blood and the blood mixes together.

What are the benefits of chorionic villus sampling?

The biggest benefit of CVS is that you get the results of genetic testing earlier in your pregnancy. Having this information allows you to make healthcare decisions sooner rather than later. For example, you can prepare for special treatment your baby may need immediately after birth. Or you may decide not to continue the pregnancy.

Another important benefit of CVS is that it’s about 99% accurate, which means you can rely on the test results.

When will I get results from CVS testing?

Your provider sends the sample of chorionic villi to a lab. Specialists in the lab grow the cells in a fluid and test them a few days later. You typically get some preliminary results within a few days. But certain conditions take longer to test for. You’ll get those results closer to 10 days to two weeks after the test. Your genetic counselor contacts you with the final results and discusses them with you — including follow-up testing, if necessary.

Is CVS testing accurate?

CVS testing is about 99% accurate. But CVS testing doesn’t detect how severe the condition is.

There are also times when the results of the test are confined to the placenta only. This means the abnormal finding affects the placenta and not the fetus. This happens in about 1% to 2% of all cases.

What happens if CVS is positive?

If the results of CVS show that the fetus has a genetic condition, you can talk with your counselor, partner and provider about how you’d like to proceed. Your provider or genetic counselor can help you best understand what the results of CVS testing mean so you can make the best decisions moving forward.

When should I call my healthcare provider?

If cramping, soreness or bleeding don’t go away or get worse after CVS testing, contact your provider. You should also get in touch with your provider if you have:

• Amniotic fluid leaking, which may feel like urine leaking.
• Chills.
• Contractions.
• Fever.

What’s the difference between CVS testing and amniocentesis?

Both CVS and amniocentesis are types of prenatal tests that look for genetic conditions in a fetus. Some of the differences between them are:

• Providers perform them at different points in pregnancy. CVS testing happens earlier in pregnancy (around 10 to 12 weeks), which means you can find out sooner if the fetus has a genetic condition. Amniocentesis happens around 16 weeks of pregnancy.
• Amniocentesis can test for neural tube defects (NTDs) like spina bifida. CVS can’t detect these conditions.
• Amniocentesis has a slightly lower risk of pregnancy loss.
• Amniocentesis can check for Rh incompatibility.
• In rare instances, you may need amniocentesis to confirm the results from a CVS.

Your healthcare provider can talk to you about your risk and recommend one of these tests, both of them or neither.

What should I ask my healthcare provider about CVS testing?

If you’re pregnant, consider asking your provider:

• Should I do prenatal testing?
• Am I at high risk for having a baby with a chromosomal or other genetic problem?
• Is CVS or amniocentesis better for me?
• What’s the risk of miscarriage?
• What are problems to look for after CVS?
• What will the results of CVS tell me?

A note from Cleveland Clinic

Chorionic villus sampling, or CVS testing, is a test to find out if the fetus has certain genetic problems. You don’t have to get CVS testing. If you choose to do so, you’ll have it when you’re around 10 to 13 weeks pregnant. The test is safe and accurate but comes with risks. The results of CVS testing can help you make important healthcare decisions. If you’re at high risk of having a baby with a genetic condition, talk to your healthcare provider. They can help you decide if CVS testing is right for you.