Understanding chorionic villus sampling

Reviewed by James Brann, MD

Chorionic villus sampling

In the most basic terms, chorionic villus sampling is a type of test in which a small piece of the placenta is taken out. The placenta is inside a woman’s uterus, and is the organ responsible for bringing nutrients and oxygen to her fetus, along with carrying out waste. The placenta and fetus will share many of the same genes.
Chorionic villus sampling, or CVS, shows if there’s something not right with a fetus’ chromosomes or genes. The chromosomes are located within cells, structures that hold thousands of genes. The CVS test will be performed between pregnancy weeks 10-13, with results expected a few days after that.

CVS is used to find out if your unborn child has a genetic problem like Tay Sachs, Down syndrome, cystic fibrosis, or some other disease. If you have any of these conditions in your family, you may have this test done. You may also have CVS if another test shows the probability your unborn child has a specific genetic problem. Doctors can’t use CVS for every genetic problem out there, though. If your test results are normal, there’s still a chance of genetic problems. The results only mean your child doesn’t have any of the conditions you were tested for.

Performing CVS

There are several steps to CVS. They include:
  • An ultrasound - This imaging test uses sound waves to make a picture of the placenta, fetus and your uterus.
  • A needle or tube - With guidance from the ultrasound picture, your doctor will then either insert a small tube into your vagina or a needle in your belly.
  • Tissue sample - After the doctor guides the tube or needle to the placenta, they’ll take a small tissue sample. They’ll then send that tissue sample off to the lab for testing.

Risks of CVS

There are some potential problems with CVS, although they are rare. Such risks may include blood leakage from the fetus into a mother’s bloodstream. This may lead to problems with other pregnancies in the future. There is also a risk of miscarriage.
Minor vaginal bleeding is normal. However, you should call your doctor about any of these symptoms:
  • Vaginal bleeding similar to a period
  • Cramps that are worsening
  • Fluid leaking from your vagina
  • A fever topping 100.4 degrees Fahrenheit (38 degrees Celsius)

Alternatives to CVS

Another test out there may be used as an alternative to CVS. Amniocentesis also tests for genetic problems in a fetus. However, amniocentesis is done a little later in your pregnancy, normally around weeks 15-17.

Whether you do CVS or amniocentesis is dependent on you and your situation. In some cases, you may not need to do either. If you do want testing, CVS has the advantage of being done sooner in a pregnancy. Because of this, you’ll get the results quicker.

On the other hand, amniocentesis brings with it a slightly smaller risk of miscarriage than CVS. You may also choose it because you’re into your second trimester; therefore, you’ve been pregnant already for more than three months.

If the test shows a specific genetic problem, you’ll want to talk with a genetic counselor. You may even want to do this before taking the test. This type of counselor will be able to help explain what you can expect, help you sort through your feelings and help you decide what to do next.

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