What is chorionic villus sampling (CVS)?

Chorionic villus sampling (CVS) is a genetic test done during pregnancy. This test checks chorionic villus cells to see if your baby has certain health conditions. Chorionic villus cells are found in the placenta (the organ that brings oxygen and nutrients to the baby).

The test looks for abnormalities in your baby's chromosomes. Chromosomes are tiny "packages" in your cells that contain your genes. Genes carry information, called DNA, that controls what you look like and how your body works. Normally, you're born with a set of 46 chromosomes, with one set coming from each parent.

The chorionic villi cells in the placenta contain the same chromosomes as your developing baby. So, a CVS test can show if your baby has an extra chromosome or a missing or damaged chromosome. These chromosome differences can cause serious health problems.

CVS is a prenatal diagnostic test, which means it can almost always tell for sure whether a developing baby has a chromosome disorder. This is different than a prenatal screening test, which only shows whether a baby has an increased risk of a serious health problem.

Other names: CVS test

What is it used for?

CVS testing is used to diagnose chromosome problems or other genetic diseases in developing baby. These include:

• Down syndrome (also called Trisomy 21), a condition in which a person has an extra chromosome or a piece of a chromosome. This extra copy changes how a baby's body and brain develop and can cause mental and physical challenges during their lifetime.
• Cystic fibrosis (CF), a disease that's inherited (passed down through families). It causes mucus buildup in the lungs and other organs, making it hard to breathe.
• Sickle cell disease (SCD), a group of inherited red blood cell disorders. SCD can cause pain, infections, organ damage, and strokes.
• Tay-Sachs disease, a disorder that causes fatty proteins to build up in the brain. It affects sight, hearing, and mental development. Most children with Tay-Sachs die by the age of 5.
• Trisomy 18 (Edward syndrome), a condition that causes the baby to have growth delays while developing. It also causes physical and mental abnormalities after they are born. Most babies with Trisomy 18 die before birth or within their first month.

CVS testing is very accurate and can be done early in pregnancy, between the 10th and 13th week. But it can only diagnose certain genetic diseases. A CVS test does not diagnose or screen for birth defects such as neural tube defects. These are conditions that cause abnormal development of a developing baby's brain and/or spine. Different tests, including an alpha-fetoprotein (AFP) blood test, are used to screen for or diagnose these and other birth defects.

Why do I need a CVS test?

A CVS test is not a routine pregnancy test. But your health care provider may recommend CVS testing if you are at higher risk for having a baby with a chromosome disorder. The risk factors include:

• Your age. If you are age 35 and older, you have a higher risk of having a baby with Down syndrome or another genetic disorder.
• A family history of a genetic disorder.
• Having another child with a genetic disorder.

You may also need CVS testing if you had abnormal results on a prenatal screening test.

What happens during a CVS test?

Your provider will use an ultrasound to check your baby's position and guide the procedure. An ultrasound is an imaging test that uses sound waves to look at your tissues and organs. The test usually takes about 30 to 45 minutes.

There are two types of CVS tests:

• Transabdominal (through your abdomen (belly)). A long, thin needle is guided through your abdomen (belly) to take a sample.
• Transcervical (through your vagina). A thin catheter is guided through your cervix, (the lower part of the uterus), to your placenta to take a sample. This is the most common method.

During a transabdominal CVS, your provider will:

• Clean your abdomen with an antiseptic.
• Apply a numbing medicine to your abdomen.
• Insert a long, thin needle through your abdomen and uterus and into the placenta. You may feel a cramping or stinging sensation as the needle enters the uterus.
• Use the needle to withdraw a sample of tissue (villi) from the placenta.
• Remove the needle.

During a transcervical CVS, your provider will:

• Clean your vagina and cervix with an antiseptic.
• Use an instrument called a speculum to gently spread apart the sides of your vagina. This is the same instrument used for a pap test.
• Insert a thin tube through your vagina and cervix and up to the placenta. You may feel a slight twinge or cramping as this is done.
• Use the tube to gently suck in a sample of tissue from the placenta.
• Remove the tube.

You may have light vaginal spotting after the procedure.

A CVS test isn't recommended if you have a sexually transmitted infection (STI) or have had vaginal bleeding during the pregnancy.

Will I need to do anything to prepare for the test?

On the morning of the test, you may be asked to drink extra fluids and not urinate. This will fill your bladder, which may help move the uterus into a better position for the procedure.

Are there any risks to the test?

CVS is generally considered to be a safe procedure, but it does have some risks. These include:

• Miscarriage (this is a small risk).
• Infection.
• Bleeding.
• Rh sensitization. This is a condition in which your body makes antibodies (proteins made by the immune system) that attack your baby's red blood cells. If diagnosed during pregnancy, it is easily treatable.
• Limb defects in the baby (this is very rare).

Call your provider if you have chills, contractions, a fever, or amniotic fluid leaking after the procedure.

What do the results mean?

CVS test results are usually available within two weeks.

If your CVS test results were normal, it is unlikely that your baby has the disorder that was tested. But it does not guarantee that your baby won't have any health problems.

If your results were not normal, it may mean your baby has a chromosome or genetic disorder, such as Down syndrome or cystic fibrosis.

Occasionally, CVS test results are unclear, and your provider may recommend amniocentesis. Amniocentesis is another prenatal diagnostic test that checks the amniotic fluid (the liquid in the sac surrounding the baby). It is performed between the 15th and 20th week of pregnancy.

If you have questions about your results, talk to your provider.

Is there anything else I need to know about CVS testing?

Some chromosome and genetic disorders require your baby to have extensive medical treatments. Other disorders may not be treatable.

If your CVS test results were not normal, you should talk with your provider about your options and the decisions you may need to make. It may also help to speak to a genetic counselor both before and after you get your results. A genetic counselor is a specially trained professional in genetics and can help you understand what your results mean.