What is chorionic villus sampling (CVS)?
- Chorionic villus sampling (CVS) is a type of prenatal diagnostic test to detect chromosomal problems that can result in genetic diseases and birth defects.
- It involves taking a small sample of part of the placenta (the chorionic villi) where it is attached to the wall of the uterus.
- CVS can diagnose chromosomal abnormalities that cause conditions like Down syndrome, sickle cell anemia, cystic fibrosis, and Tay Sachs disease. It does not diagnose neural tube defects.
- Because the procedure examines genetic material, it can tell you the gender of the fetus.
- CVS is performed earlier in pregnancy than amniocentesis. It is done between the 10th and 13th week of pregnancy (measured from your last menstrual period). It is reported to be 98% to 99% accurate in detecting genetic abnormalities.
- CVS can also be used to detect paternity and is 99% accurate in establishing paternity of a fetus.
How is CVS performed?
Samples for CVS are taken in one of two ways:
- Transabdominal: In this method, similar to amniocentesis, a long, thin needle is inserted through the abdominal wall into the placenta, guided by ultrasound images.
- Transcervical: With the transcervical method, a long, thin tube is passed into the vagina and up into the uterus to obtain the sample by suction. This method is most common.
The procedure can be completed in about half an hour. The actual sampling process only takes a few minutes. There may be mild discomfort when the sample is taken. After the test you may have mild cramping and bleeding, and you should rest the day of the procedure. You may be asked to abstain from sex and vigorous activity for a few days after the test. You should contact your doctor if you experience fever, heavy vaginal bleeding or cramping, or leakage of fluid from the vagina after the test.
After the sample is removed, the cells are cultured in a laboratory and analyzed. It typically takes 7 to 10 days before results are available.
What are the benefits and risks of CVS?
A major benefit of CVS is that it can be performed earlier in the pregnancy than amniocentesis, providing information about genetic defects earlier in the pregnancy. If a woman chooses termination of pregnancy, it is safer at earlier stages of pregnancy.
Miscarriage is the main risk associated with CVS and occurs in 1 out of every 100 cases. The risk of miscarriage can be slightly greater than the risk of miscarriage associated with amniocentesis. Rarely, defects in the fingers or toes of the fetus have been reported with CVS, but these cases were particularly common when CVS was done very early in pregnancy, before 9 weeks' gestation. For this reason, most cases of CVS are performed only at or after 10 weeks' gestation. Infection is another uncommon complication of CVS.
Who should receive CVS testing?
CVS testing is generally offered to women or couples who have one of the following:
- Women aged 35 or greater
- Couples with a family history of genetic disorders or birth defects
- Women with other abnormalities found in prenatal testing
Genetic counseling and a full discussion of the risks and benefits of the procedure are recommended before undergoing CVS testing.
Some women should not receive CVS testing. CVS testing is typically not recommended for:
- Multiple gestations
- Women with an active infection, such as a sexually-transmitted disease
- Women who have had vaginal bleeding during the pregnancy
Additionally, women with uterine fibroids or a tilted uterus may not be good candidates for transcervical CVS testing.
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