Chorionic villus sampling often referred to as CVS, is a diagnostic test for identifying chromosome abnormalities and other inherited disorders. This test may be recommended by your health care provider if you or your partner has family medical histories that reveal potential risks.
How is the chorionic villus sampling (CVS) performed?
CVS is a diagnostic procedure which involves removing some chorionic villi cells from the placenta at the point where it attaches to the uterine wall.
There are two ways samples are collected:
Transcervical: An ultrasound guides a thin catheter through the cervix to your placenta. The chorionic villi cells are gently suctioned into the catheter. This is the most common method.
Transabdominal: An ultrasound guides a long thin needle through the abdomen to your placenta. The needle draws a sample of tissue and then is removed. This procedure is similar to that of amniocentesis.
The CVS procedure collects larger samples and provides faster results than amniocentesis. Results may be received between one to seven days.
When is chorionic villus sampling (CVS) performed?
CVS is usually performed between 10 and 13 weeks from your last menstrual period. CVS may be chosen over amniocentesis because it may be performed earlier in the pregnancy.
What does the test look for?
Chorionic villus sampling detects chromosome abnormalities (i.e. Down syndrome) and genetic disorders (i.e. cystic fibrosis.). This test is different from amniocentesis in that it does not allow for testing for neural tube defects.
Chorionic villus sampling also provides access to DNA for paternity testing prior to delivery. DNA is collected from the potential father and is compared to DNA obtained from the baby during chorionic villus sampling. The results are accurate (99%) for determining paternity.
What do chorionic villus sampling (CVS) results mean?
CVS is a diagnostic test that detects chromosome abnormalities and genetic disorders with high levels of accuracy (98-99%). Although the probabilities of identification are high, this test does not measure the severity of these disorders. This test does not help identify neural tube defects.
Are there risks or side effects to the mother or baby?
Although CVS is considered to be a safe procedure, it is recognized as an invasive diagnostic test that does pose potential risks. Miscarriage is the primary risk related to CVS occurring 1 out of every 100 procedures.
CVS is not recommended for women who:
- Have an active infection (i.e. STD)
- Are carrying twins
- Have experienced vaginal bleeding during pregnancy
Transcervical CVS is not recommended for women who:
- Have uterine fibroids
- Have a tilted uterus which impedes the catheter
Following the procedure, the mother may experience one or more of the following side effects:
Contact your healthcare provider if these symptoms remain or get worse.
You should also contact your healthcare provider if you experience:
- Leaking of amniotic fluid
According to the Mayo Clinic, there is a 1% chance of getting false positive results. A false positive occurs when the test indicates that the fetus has an abnormality, but it actually does not.
What are the reasons to test or not test?
The reasons to test or not test vary from person to person and couple to couple.
Performing the tests and confirming the diagnosis provides you with certain opportunities:
- Pursue potential interventions that may exist
- Begin planning for a child with special needs
- Start addressing anticipated lifestyle changes
- Identify support groups and resources
- Make a decision about carrying the child to term
Some individuals or couples may elect not to pursue testing or additional testing for various reasons:
- They are comfortable with the results no matter what the outcome is
- Because of personal, moral, or religious reasons, making a decision about carrying the child to term is not an option
- Some parents choose not to allow any testing that poses any risk of harming the developing baby
It is important to discuss the risks and benefits of testing thoroughly with your healthcare provider. Your healthcare provider will help you evaluate if the benefits from the results could outweigh any risks from the procedure.
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Compiled using information from the following sources:
1. Mayo Clinic Complete Book of Pregnancy & Baby’s First Year. Johnson, Robert V., M.D., et al, Ch. 11.
2. Williams Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 13.