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Chorionic (kor-ee-ON-ic) villus sampling— or CVS for short—is a medical test for pregnant women. CVS is usually performed between the 10th and 13th weeks of pregnancy to see if the baby has certain conditions such as Down syndrome.
It is a genetic test. Genetic testing is used to look for certain genetic diseases, chromosome problems, and birth defects. Your doctor and/or a genetic counselor can help to determine which test or tests are right for you. This depends on factors such as your age, your family and medical history, and environmental exposures. Although genetic testing cannot answer all questions about the health of your developing baby, it can provide information to help you and your partner make informed decisions.
Each cell of your body has chromosomes that carry the blueprint for your whole body. The chromosomes carry the traits (such as eye or hair color) that you inherited from your mother and father. Normally, each cell contains 46 chromosomes. Having too much or too little chromosome material often results in health problems.
CVS takes a small sample of cells from tiny finger-like growths (called chorionic villi) in the placenta. These cells have the same chromosomes as the baby. Careful testing of these cells is done to look for problems.
Previous recommendations stated that women who are 35 years or older at the time of delivery should consider CVS. However, in 2007 the American College of Obstetricians and Gynecologists (ACOG) released new recommendations stated the following.
Additionally, CVS should be considered for the following:
The CVS procedure is guided by ultrasound. Ultrasound uses sound waves to produce a “picture” of the baby. Ultrasound helps the doctor tell how far along the pregnancy is. It shows if you are carrying more than 1 baby. It also shows the position of the placenta.
For the ultrasound, you will lie on a table in an examination room. A gel will be spread on your belly to help the sound waves pass through your belly. You will probably be able to see your baby’s image on the screen.
There are 2 ways that CVS can be done. Your doctor will determine which method to use depending on the position of the placenta. They are:
The CVS procedure, including the ultrasound, takes less than 1 hour. You will not have to stay overnight at the hospital.
As with many medical procedures, there are risks associated with CVS. These risks include infection and vaginal bleeding. Recent studies have suggested that in experienced centers, the risk for miscarriage or loss of the pregnancy from the procedure itself is approximately 1 in every 1,000 procedures performed. There is no evidence that it slows the growth of the developing fetus. Your doctor will go over the risks with you. You will be asked to sign a consent form before agreeing to have CVS and genetic testing. The consent form will describe the risks as well.
There are several reasons why it may not be possible to perform CVS. They include:
No. It is important to remember that all couples have a 2 to 3 percent risk of having a child with a birth defect. This means that in general, among every 100 babies born, 97 or 98 will be normal and 2 or 3 will have a birth defect.
Many birth defects are not due to chromosome disorders. CVS cannot detect these types of birth defects.
While CVS can detect many chromosome disorders and some genetic disorders, it cannot detect certain birth defects such as spina bifida (open spine) and anencephaly (open skull). A detailed ultrasound exam and/or another test, called multiple marker screening or AFP, is recommended at 15 to 21 weeks of pregnancy to test for these conditions.
If a disorder is found, your doctor will explain your options. At UPMC, counseling and support are available to help you make an informed decision. Several medical options are available, including referral to experts who are familiar with the treatment and management of specific conditions.
If you have additional questions about this information or think you may want chorionic villus sampling, please call the UPMC Center for Medical Genetics at 412-641-4168 or 1-800-454-8155.
Revised September 2011