|
By Lila Havens, Staff Writer
Chorionic villus sampling (CVS) is a prenatal test that can diagnose many types of chromosome and genetic problems, including Down syndrome. In CVS, A doctor inserts a catheter or thin needle into the uterus to take a sample of the chorionic villi. These are tiny fingerlike projections that will become the placenta. The chorionic villi contain the same chromosomes as the fetus.
Why would I have CVS?
You may want to have this test if you are at risk for having a baby with chromosomal or genetic birth defects, and you wish to get the test results quickly. Prenatal genetic testing may be offered if you:
- Are 35 or older. The risk of having a baby with Down syndrome and other genetic defects increases as a woman ages.
- Already have a child with a chromosome defect.
- Have a family or personal history of inherited genetic disorders that CVS can identify, such as Tay-Sachs disease, sickle cell disease or cystic fibrosis.
- Had an abnormal fetal ultrasound exam.
CVS is not offered to all pregnant women because it does have some risks. It is offered when the risk of a genetic disorder is judged to be greater than the risks from the test. Other, noninvasive screening tests may be a better option for women with normal risks.
You may want to seek genetic counseling, especially if you have any inherited risk factors. A genetic counselor can help you understand your risks and decide on the proper testing.
How is CVS done?
CVS may be done either through the cervix or through the abdomen.
-
Transcervical CVS. First, the vagina is cleaned with an antiseptic. Using ultrasound as a guide, the doctor threads a thin tube through the vagina and cervix and uses gentle suction to remove a small sample of the chorionic villi.
-
Transabdominal CVS. The doctor inserts a long thin needle through the abdominal wall, using ultrasound to guide the needle. This is similar to the way amniocentesis is done.
Cramping and spotting are common for the first day or so after CVS. Call your doctor if you have a fever, heavy bleeding or any symptoms that worry you.
How reliable are the results?
CVS is more than 99 percent accurate at ruling out certain chromosomal birth defects and genetic problems. Sometimes other tests are needed to confirm the results.
It's important to note that no test, including CVS, can identify all possible genetic disorders or guarantee a healthy baby.
What are the risks of CVS?
CVS is generally very safe, with a low rate of complications (about one in 100, or 1 percent). Possible complications include miscarriage, vaginal bleeding and infection. These risks are lower for doctors who do CVS often.
In the 1990s, CVS done before the 10th week of pregnancy sometimes caused defects in babies' fingers and toes. Now CVS is routinely done between 10 and 12 weeks of pregnancy. Studies have found no higher risk of these defects when CVS is done at or after the 10th week of pregnancy.
Is there another test that gives the same information?
Amniocentesis can give similar results. There are a couple of differences between CVS and amniocentesis:
- CVS is done earlier than amniocentesis - in the first trimester, between the 10th and 12th weeks of pregnancy. Amnio is done between the 15th and 22nd weeks. Many women want to have these results as soon as possible.
- CVS does not screen for neural tube defects, which occur when the spine doesn't close properly. Amniocentesis does. Women who choose CVS can have a blood test in the second trimester to check for these defects.
- CVS is a newer technique than amniocentesis, and it is not as widely available.
Both CVS and amniocentesis are invasive tests that carry a small risk of miscarriage and other complications. Your doctor can help you weigh the risks and decide which test might be best for you.
|
Related Articles
|
|
External Sources
|
This article was reviewed and updated
08-01-2009.
Return to the previous page
|
