What is chorionic villus sampling?

Chorionic villus sampling (CVS) is a method of prenatal diagnosis, which is a way to directly test for genetic conditions in the fetus.

During the CVS test, a small sample of cells (called chorionic villi) is taken from the placenta where it attaches to the wall of the uterus. Chorionic villi are tiny parts of the placenta that are formed from the fertilized egg, so they typically have the same genes as the fetus.

If you have certain risk factors, you may be offered CVS as a way to detect genetic conditions during early pregnancy. Whether you choose to have the test is up to you.

What diseases or disorders can chorionic villus sampling identify?

CVS can help identify chromosomal problems such as Down syndrome or other genetic diseases such as cystic fibrosis, Tay-Sachs disease, and sickle cell disease. CVS does not detect birth defects. An ultrasound performed later in the pregnancy (18-20 weeks) will usually check for most birth defects. If you have CVS, you may want to consider having a blood alpha-fetaprotein (AFP) test later in pregnancy to screen for neural tube (brain, spine, or spinal cord) defects.

What are the benefits of chorionic villus sampling?

CVS can be done earlier in pregnancy than amniocentesis. Getting this kind of information early allows a woman to make choices in the beginning stage of her pregnancy. If a woman chooses to end her pregnancy after receiving abnormal test results, the pregnancy termination will be safer than if she waits for amniocentesis results.

What are the potential risks of chorionic villus sampling?

CVS may carry a slightly higher risk of miscarriage than amniocentesis, since the procedure is done in early pregnancy. The risk for pregnancy loss (miscarriage) related to a CVS is about 1 in 200. Infection may also be a complication. Rare cases of limb deformities in infants have been reported, but most of these have been related to doing the CVS prior to 10 weeks gestational age.

Who should have a chorionic villus sampling test?

Testing should be offered to:

  • Pregnant women who will be 35 or older on their due date (the risk of having a baby with a chromosomal problem such as Down syndrome increases with the age of the woman)
  • Couples who already have had a child with a known genetic condition or have a family history of a genetic condition
  • Pregnant women at risk to have a child with a particular genetic condition based on abnormal or positive screening results

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