Chorionic villus sampling (CVS) is a prenatal test that checks for serious chromosome disorders in the developing baby. The test involves taking a sample from the chorionic villi, a part of the placenta, and analyzing the genetic makeup of the tissue.
Comparison to Amniocentesis:
Older statistics showed that the CVS test carried a higher risk of miscarriage than amniocentesis, but research shows that the risk is about the same (roughly 1 in 400). The main benefit of CVS is that it can be performed earlier in pregnancy (around 10 to 12 weeks), but the downside is that CVS is more likely than amniocentesis to show inconclusive results and also cannot offer information on neural tube defects.
Who Should Have the Test:
CVS is usually offered to moms who have a higher than average risk of having a baby affected by a serious genetic disorder, such as those who are known carriers for conditions like Tay-Sachs Disease or severe metabolic disorders. So, they can then have an answer as early as possible on whether or not the baby has the disorder. Because screening tests such as alphafetoprotein results or the triple/quad screen test are usually done later in pregnancy anyway, most moms with concerning results on these tests will be offered an amniocentesis rather than a CVS test.
What the Results Tell You:
A CVS test can detect chromosome disorders and genetic abnormalities in the placental tissue. In contrast to an amniocentesis, a CVS cannot provide information neural tube defects. Note that although the CVS test can detect Down syndrome, it is not exclusively a test for Down syndrome -- there are many serious conditions that parents may be concerned about when they consider a CVS. A CVS test is considered about 99% accurate for diagnosing genetic disorders.
What to Expect From the Test:
A CVS may be performed either transabdominally or transcervically; the latter is similar to having a pap smear. A transabdominal CVS involves a long needle through the abdomen similar to an amniocentesis. You do not need to do anything specific to prepare for the test in most cases. The test can be painful but is usually over in a few minutes.
Considering a CVS Test:
If your doctor has recommended that you have a CVS test, don't be afraid to ask a lot of questions if you have them. It is normal to be apprehensive about having prenatal tests done that may carry a risk of miscarriage, and it is fine to decline these tests if you are not comfortable with that risk. Do note, however, that newer research suggests that the actual risk of miscarriage after a CVS or an amniocentesis is much lower than the older estimates -- and that physicians who perform the procedure regularly are likely to have the lowest miscarriage rates.
Many parents are uncomfortable with the risks of a CVS, or may have a stance that they would not terminate a pregnancy regardless of the results. So the test is not worth pursuing. These viewpoints are perfectly valid, especially since the CVS merely provides information and usually there is no prenatal treatment for the disorders diagnosed through CVS. Other parents prefer to wait a few extra weeks and have an amniocentesis instead if the triple/quad screen test or ultrasound test seems to indicate problems, given that the amniocentesis can also evaluate for neural tube defects. As stated above, the parents who should most consider a CVS are those who have a high risk of conceiving a baby with a serious disorder and a desire to confirm or rule out the diagnosis as early as possible.
Chorionic Villus Sampling: CVS. American Pregnancy Association. Accessed: Mar. 12, 2009. http://www.americanpregnancy.org/prenataltesting/cvs.html.
Chorionic Villus Sampling (CVS). March of Dimes. Quick Reference: Fact Sheets. Accessed: Mar. 12, 2009. http://www.marchofdimes.com/professionals/14332_1165.asp.