Chorionic villus sampling (CVS)
At Children’s Hospital of Wisconsin, we perform chorionic villus sampling to help parents-to-be rule out certain genetic conditions. We test this tissue to help determine the health of your unborn baby. Doctors perform this test early in the pregnancy, usually between 10 and 13 weeks.
What is chorionic villus sampling (CVS)?
Chorionic villus sampling, or CVS, is a procedure in which a small sample of tissue is removed from the placenta. Genetic testing of this tissue can help you rule out certain health problems in your unborn baby. Doctors perform this test early in a pregnancy, usually between 10 and 13 weeks.
Who should undergo CVS?
If you are at higher-than-average risk to have a child with a genetic condition that may be discovered by this testing, you should consider CVS.
Common reasons for testing include:
- Mother is 35 or older at the time of delivery with one baby, or 33 years old or older at the time of delivery of more than one baby
- A family history of a genetic condition, such as Down syndrome or cystic fibrosis
- An abnormal finding on ultrasound examination
- Both parents are carriers of a genetic condition, such as Tay Sachs disease or sickle cell disease
If the identity of the father is in question, you can use DNA from the CVS to perform a paternity test.
What is the chorion?
The chorion is part of the developing placenta. Chorionic villus sampling takes a small amount of this tissue from the placenta and uses the cells from the chorion for genetic testing.
What does a test of the chorion tell me about the health of my unborn baby?
The cells from the placenta can give us information about your baby's genes and chromosomes because your baby and the placenta formed from the same fertilized egg. When the egg and sperm came together to start the pregnancy, they formed the first cell. This cell divided many times. As those cells divided, some of them became the chorion, and some became the baby. This is why the chorion has the same genetic makeup as your baby.
What tests are usually included in the genetic testing of CVS tissue?
The test most often performed on CVS tissue is a chromosome analysis, a test for disorders such as Down syndrome. Testing for specific genetic disorders, such as cystic fibrosis, can be done on the same sample. Even paternity testing can be performed.
How do you perform CVS?
There are two ways to perform CVS – transabdominally and transcervically. The approach that we take depends on an ultrasound that is performed to determine the location of the villi in the uterus.
- The transabdominal approach uses a needle. For this procedure, you lie on the examination table. We clean your skin with an antiseptic solution. Under ultrasound guidance, we guide the needle through your abdominal wall and the wall of the uterus to reach the villi (tiny outgrowths on the uterus wall). We then use a syringe attached to the needle to suction out a small amount of villi as the needle passes through the villi.
- The transcervical approach uses a thin, flexible plastic catheter (a hollow tube). For this procedure, you lie on your back in a gynecologic examination position. We insert a gynecologic speculum into your vagina so we can see your cervix (the opening to the uterus). We clean your vagina with an antiseptic solution, and then, with ultrasound guidance, we carefully move the catheter through the cervix to the villi. As we withdraw the catheter, we suction out a small amount of villi with a syringe attached to the catheter. If we do not obtain an adequate amount of tissue with the first attempt, we may make a second attempt. In studies of CVS, the risk of miscarriage rose with 3 or more attempts(1).
Is CVS right for me?
For some women, the position of the uterus and the villi within the uterus do not permit testing. In many cases, waiting one to two weeks for growth to occur may allow testing. A few individuals will have to wait for an amniocentesis to be performed later in the pregnancy to gather genetic information about the fetus.
There are some women who should not have this testing. Your doctor will discuss whether CVS is right for you if:
- You have had bleeding during this pregnancy
- You have been told that you have an abnormality of the uterus, such as a bicornuate uterus
- You have active genital herpes
Which CVS approach will I have?
The approach your doctor chooses will depend upon the position of your uterus and the position of the villi within the uterus. When the villi are anterior (closer to your front), we generally perform the test transabdominally. When the villi are in the lower part of the uterus and closer to your back, we generally perform the test transcervically.
Your doctor will use an ultrasound examination at the time of the procedure to determine which way will be easiest. At that time, he or she will discuss the plan with you.
After the procedure, doctors will perform another ultrasound to check your baby’s heartbeat.
Are transabdominal and transcervical CVS equally safe?
Yes. In a study in 1992, researchers found that the risk of miscarriage was equal with these two approaches. However, researchers noticed that vaginal bleeding after the procedure was more common with the transcervical approach(2).
What are my alternatives to CVS?
The primary alternative to CVS is amniocentesis, which is usually performed at about 16 weeks gestation. Early amniocentesis can be performed starting at 13 to 14 weeks.
The risks of amniocentesis include:
- Leakage of amniotic fluid
- Injury or infection of the fetus
- Infection, internal bleeding or injury to other organs in the mother
Amniocentesis can result in the mother developing Rh incompatibility, which is a blood incompatibility between the unborn baby and the mother that can affect future pregnancies. Some individuals learn about all of the different prenatal testing options and choose not to have any invasive testing.
How long does CVS take, and what does it feel like?
- When performed transcervically, the procedure usually takes no more than a couple of minutes, and women generally experience discomfort similar to that of a pap smear.
- When performed transabdominally, the procedure usually takes less than a minute, and most women experience a heavy pressure sensation in their abdomen.
You will not need anesthesia for either procedure.
What are the advantages of CVS?
CVS allows you to know about the health of your baby earlier in the pregnancy. In contrast, you likely won’t receive results from an amniocentesis until you are 17 to 18 weeks into the pregnancy.
What are the risks of CVS?
There are a number of risks of CVS, including:
- Miscarriage: CVS carries a slightly higher rate of miscarriage than amniocentesis. The rate of miscarriage is 1 in 100 to 1 in 200 for CVS compared to 1 in 200 to 1 in 400 for amniocentesis.
- Inconclusive results: There is a small chance that we may find a mixture of normal and abnormal cells in your CVS. In most instances, these abnormal cells are confined to the placenta and are not in the baby. In these situations we perform an amniocentesis to determine whether the abnormal cells are present in the baby.
- Potential for missed diagnoses: CVS cannot detect spina bifida or other neural tube defects. We recommend that women have maternal serum alpha-fetoprotein (AFP) screening in addition to CVS. This blood test is performed at 15 to 18 weeks of pregnancy.
Years ago, there was some concern that CVS can cause a small increase in the risk of limb abnormalities(3),but there is substantial evidence showing this is not true.
What can I expect after a CVS?
Mild pain: Some individuals experience soreness or mild cramping for a day after the procedure. Spotting or vaginal bleeding also may occur. This bleeding may initially soak a pad or more for the first few days. We expect that the bleeding will decrease over several days. The bleeding initially will be red and then change to brown.
Down time: We recommend that you take it easy for two days. If you are on your feet a lot, we encourage you to take off for two days or alter your home and/or work schedule to allow you to sit rather than stand or walk. We can provide a written excuse for your employer.
What should I look out for after CVS?
If you have any questions or symptoms that are of concern to you after your CVS, please talk with your doctor.
Symptoms of complications include:
- Severe cramping
- Increasing bleeding
- Leakage of clear fluid
- Increasing soreness
- Tenderness in the abdomen
If you experience any of the above symptoms after CVS, contact your doctor right away.
When will my CVS test results be ready?
Testing for chromosomal abnormalities such as Down syndrome usually take about 10 to 14 days. Other specialized testing, such as DNA testing or biochemical analysis, may take longer.
If your results are abnormal, we will discuss them with you, as well as any additional testing we recommend.
Do normal results from a CVS guarantee that I will have a healthy baby?
More than 95 percent of the high-risk women who have CVS or amniocentesis receive reassuring news – that their unborn babies do not have the disorders for which they were tested. However, no prenatal tests can guarantee the birth of a healthy baby since only certain conditions can be ruled out before birth. Three or four out of every 100 babies have a birth defect.
There is no test available that guarantees you will have a healthy baby. Normal CVS and amniocentesis results help to exclude some potential problems, so they are reassuring. Only after your baby's birth will you know just how healthy he or she is.
Learn more about CVS and other common tests during pregnancy.
- Rhoads GG, Jackson LG, Schlesselman SE et al. The Safety and efficacy of Chorionic Villus Sampling for Early Prenatal Diagnosis of Cytogenetic Abnormalities. N Engl J Med 1989;320:609-617.
- Jackson LG, Zachary JM, Fowler SE et al. A Randomized Comparison of Transcervical and Transabdominal Chorionic Villus Sampling. N Engl J Med 1992;327:594-598.
- Evaluation of Chorionic Villus Sampling: WHO/PAHO Consultation on CVS. Prenatal Diagnosis 1999; 19:97-99.