Chorionic villus sampling (CVS) is test for pregnant women that checks chorionic villi, tiny finger-like growths found in the placenta. The placenta is the organ that nourishes an unborn baby in the uterus. The test looks for abnormalities in the baby’s chromosomes. Chromosomes are parts of cells that contain your genes. Genes are parts of DNA passed down from your mother and father. Normally, people have a total of 46 chromosomes.
Chorionic villi contain the same chromosomes as an unborn baby. So, a CVS test can show if a 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 an unborn 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 an unborn baby. These include:
- Down syndrome, a disorder that causes intellectual disabilities, certain physical features, and various health problems.
- Cystic fibrosis, a disease that causes mucus buildup in the lungs and other organs, making it hard to breathe.
- Sickle cell disease, a disorder of the red blood cells. It 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.
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, 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?
You may need CVS testing if you are at higher risk for having a baby with a chromosome disorder. Risk factors include:
- Age. Women age 35 and older have a higher risk of having a baby with Down syndrome or another genetic disorder.
- 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?
There are two types of CVS tests:
- Transabdominal The sample is taken through the abdomen.
- Transcervical. The sample is taken through the cervix. The cervix is the lower, narrow end of the uterus that opens into the vagina.
Your provider will use an ultrasound to check your baby’s position and guide the procedure (transabdominal or transcervical). Ultrasound is an imaging test that uses sound waves to create pictures.
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 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.
- 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.
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, which happens in about one in every hundred procedures
- 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)
What do the results mean?
CVS test results are usually available within two weeks.
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. It is performed between the 15th and 20th week of pregnancy.
If you have questions about your results, talk to your health care 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 health care 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.
Courtesy of MedlinePlus from the National Library of Medicine.