Chorionic villus sampling (CVS) is a test that can find certain problems with your fetus. These include many diseases that run in families (genetic disorders) and chromosome defects. It is done during early pregnancy, most often between the 10th and 12th weeks.
Chorionic villi are tiny finger-shaped growths found in the placenta. The chorionic villus cells have the same genetic material as the baby's cells. During CVS, a sample of the chorionic villus cells is taken. The sample is collected by putting a thin tube (catheter) through the vagina or by putting a long, thin needle through the belly. Ultrasound is used to guide the catheter or needle to the right spot.
CVS is done earlier in pregnancy than amniocentesis (usually done at 15 to 20 weeks). And the results of CVS are available sooner. This gives you more time to make decisions about your pregnancy or plan for the future.
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Why It Is Done
You may choose to have this test because:
- Of your age. As you get older, you have a greater chance of having a baby with a birth defect.
- You or the baby's father carries an abnormal gene that can cause an inherited disease, such as Tay-Sachs disease, sickle cell anemia, or cystic fibrosis.
- You or the baby's father has a family history of a genetic disorder or birth defect.
- You have already had a child who has Down syndrome or another chromosome defect.
- Other tests suggest that your chance of having a baby with a genetic disorder or birth defect is higher than average.
- You want to know if your baby has a serious health problem. This may help you decide early if you want to continue the pregnancy and make plans to care for a sick child.
How To Prepare
You may be asked to drink a glass of fluid about an hour before the test. This is so your bladder will be full. A full bladder makes it easier to do the test.
You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
Be sure to tell your doctor before the procedure if you are allergic to any medicines, such as numbing medicines (local anesthetics).
Talk to your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
How It Is Done
CVS is usually done by a perinatologist. It may be done in the doctor's office or the hospital. An overnight stay in the hospital usually is not needed.
Through the belly (transabdominal)
You will lie on your back on an exam table with your belly bare.
Ultrasound will be used to help your doctor guide the needle to the placenta. Gel will be rubbed on your belly. An ultrasound device (transducer) will be moved over your belly. It gives off and picks up sound waves. The sound waves are sent to a computer to make a picture of your uterus, your baby, and the placenta on a screen. The doctor can also use ultrasound to check your baby's heart rate. For more information, see the topic Fetal Ultrasound.
Your skin where the needle will be put in is cleaned with alcohol and numbed with a medicine. Your doctor then puts a long, thin needle through your belly and uterus to the placenta. The needle is used to collect a sample of the chorionic villus cells.
Through the cervix (transcervical)
You will take off your clothes below the waist. You will have a paper or cloth covering around your waist. You will lie on your back on an exam table with your feet raised and supported by stirrups.
Your doctor will put a special tool with curved sides (speculum) into your vagina. The speculum gently spreads apart the vaginal walls. This lets the doctor see the inside of the vagina and the cervix. The cervix will be cleaned with a special soap.
Your doctor will use ultrasound to guide a thin tube (catheter) through your cervix to the placenta. Gel will be rubbed on your belly. An ultrasound device (transducer) will be moved over your belly. It gives off and picks up sound waves. The sound waves are sent to a computer to make a picture of your uterus, your baby, and the placenta. The doctor can also use ultrasound to check your baby's heart rate. For more information, see the topic Fetal Ultrasound.
When the catheter is in the right place, a sample of chorionic villus cells will be collected.
After the sample is collected, the doctor may listen to your baby's heart and check your blood pressure, pulse, and breathing.
How It Feels
Through the belly (transabdominal)
You will feel a short, sharp sting from the needle used to give the numbing medicine. There is usually no pain when the collecting needle is put in the belly. You may have some cramping when the needle is in your uterus.
Through the cervix (transcervical)
CVS may cause cramping, leakage of amniotic fluid, and vaginal spotting. These will go away in 1 to 2 days. If you had the belly procedure, you may feel some soreness where the needle was put in.
CVS also increases the risk of:
- Infection in your uterus.
- Miscarriage. One study showed the risk of miscarriage is only about 1 in 400 when the test is done by a highly trained doctor.1
- The baby being born with an arm or leg defect. But this rarely happens, especially if the test is done after 10 weeks.
There is a very small chance that CVS could cause bleeding that could let your blood mix with your baby's blood. If you have Rh-negative blood, you will be given the Rh immunoglobulin vaccine (such as RhoGAM). This can prevent Rh sensitization, which could harm your baby if he or she has Rh-positive blood.
After the procedure
It is normal to have mild cramping and vaginal spotting and to leak a little amniotic fluid for the first day or two after the procedure.
Call your doctor right away if you have:
- Moderate or severe belly pain or cramping.
- More leakage of amniotic fluid from your vagina.
- More vaginal bleeding than spotting, or bright red bleeding.
- Chills or a fever.
- Redness or swelling at the needle site if you had a belly procedure.
The genetic material (chromosomes) of the cell sample is looked at carefully. Normally there are 46 chromosomes in each cell, arranged in 23 pairs. The number and arrangement of the chromosomes in the sample can show if your baby has a genetic disease. Chromosomes also show the sex of your baby.
It may take 1 to 2 weeks to get CVS results.
No abnormalities are found in the genetic material of the chorionic villus cells.
Abnormalities are found in the genetic material of the chorionic villus cells.
What Affects the Test
Your doctor will talk with you about anything that might keep you from having the test or that may change the test results.
What To Think About
- CVS can find certain problems, but normal results don't guarantee that your baby will be healthy. No test can do that.
- Amniocentesis can find some diseases that CVS can't find, such as neural tube defects. It is done later in pregnancy than CVS (usually at 15 to 20 weeks). If CVS results are not clear or if you are worried about neural tube defects, you may decide to have amniocentesis. For more information, see the topic Amniocentesis.
- In rare cases, the chorionic villus cells may have abnormal genetic material even though the baby's cells are normal. This is called a false-positive result. An abnormal test result may need to be confirmed by amniocentesis.
- There is a very small chance that CVS could cause bleeding that could let your blood mix with your baby's blood. If you have Rh-negative blood, you will be given the Rh immunoglobulin vaccine (such as RhoGAM). This can prevent Rh sensitization, which could harm your baby if he or she has Rh-positive blood.
- If you have a vaginal infection (such as a yeast infection or herpes), CVS will be done through the belly instead of through the vagina.
- If CVS finds that your baby has a problem, it may be helpful to talk with your doctor and a genetic counselor. They can help you understand the health problem and what to expect when your baby is born.
Other Works Consulted
American College of Obstetricians and Gynecologists (2007, reaffirmed 2008). Screening for fetal chromosomal abnormalities. ACOG Practice Bulletin No. 77. Obstetrics and Gynecology, 109(1): 217-227.
Cunningham FG, et al. (2010). Prenatal diagnosis and fetal therapy. In Williams Obstetrics, 23rd ed., pp. 287-311. New York: McGraw-Hill Medical.
Wapner RJ, et al. (2009). Prenatal diagnosis of congenital disorders. In RK Creasy et al., eds., Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice, 6th ed., pp. 221-274. Philadelphia: Saunders Elsevier.
Primary Medical ReviewerSarah Marshall, MD - Family Medicine
Specialist Medical ReviewerSiobhan M. Dolan, MD, MPH - Reproductive Genetics
Current as ofMay 22, 2015