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Chorionic Villus Sampling (CVS)

What is chorionic villus sampling?

Chorionic villus sampling (CVS) is a test that may be done early in pregnancy (usually between the 10th and 13th weeks of pregnancy) to test the baby's genetic information (chromosomes). For the test, a small sample of tissue is removed from the placenta. The genetic information in the placenta tissue is the same as the baby's genetic information. Genetic specialists analyze the tissue. The test can help you know early in a pregnancy if the baby has a chromosome problem, such as Down syndrome.

When is it used?

You may consider having CVS because:

  • You will be 35 or older on the baby's due date.
  • First-trimester ultrasound or blood tests suggest the baby may have a problem.
  • You or the baby's father may have a family history of problems that can be found with genetic tests.
  • You have had a previous pregnancy or child with a birth defect.
  • You have had 3 or more miscarriages.
  • You have male relatives with genetic diseases such as hemophilia or muscular dystrophy.

Amniocentesis is another test that can check the baby's genetic information, but it is done later in pregnancy. Amniocentesis is a procedure in which fluid is sampled from inside the sac that surrounds the baby. Amniocentesis is usually done between the 15th and 18th weeks of pregnancy. CVS is used to test for many of the same problems that amniocentesis tests for. Unlike amniocentesis, however, CVS cannot detect neural tube defects, which are birth defects of the baby's brain or spine. A blood test (alpha-fetoprotein/AFP screening) may be done to test for neural tube defects later in the pregnancy.

How do I prepare for this test?

CVS is usually done 10 to 13 weeks after your last menstrual period. If you have had any spotting or bleeding, or if you are not sure of the date of your last menstrual period, you will have an ultrasound exam before you have CVS to determine more accurately how long you have been pregnant. This is important for proper interpretation of the test results.


If you have a vaginal infection, it should be treated before the test. For this reason, your healthcare provider will check for infection with cultures of the cervix before the test. CVS can be done if the cultures show that you do not have an infection.

What happens during the procedure?

CVS is performed in 1 of 2 ways:

  • through the vagina into the cervix (transcervical CVS) or
  • through the belly (transabdominal CVS).

For the transcervical test, a thin plastic tube called a catheter is inserted into the vagina and through the cervix to reach the placenta. Ultrasound is used to help guide the tube. The tube is used to get a small sample of placental chorionic villus tissue.


For transabdominal CVS, a needle is inserted through the abdomen and uterus and into the placenta. Ultrasound is used to help guide the needle. The needle and a syringe are used to get a small amount of tissue. This method for getting tissue is similar to amniocentesis. It is used more often than the transcervical test.

What happens after the procedure?

Avoid strenuous activity for 1 to 2 days after the test. You may have a small amount of bloody spotting for up to a week, particularly if you had the transcervical procedure.


You may have some results of the test in 3 to 4 days. You can usually expect the final results within 2 weeks.

What are the benefits of this procedure?

CVS can be done earlier in pregnancy than amniocentesis. With CVS, you can usually have the results of genetic tests before the 14th week of pregnancy. If the test finds a genetic problem, you and your healthcare provider will discuss your options for treatment. The information can help you decide how to manage a pregnancy with a baby that may be affected by the problem.

What are the risks and disadvantages associated with this procedure?

  • The biggest risk is miscarriage after the procedure. Miscarriages occur after CVS in about 1 of every 100 procedures. This is slightly higher than the risk with amniocentesis, which is about 1 in 200 procedures.
  • Other problems that can occur from CVS are bleeding, cramping, leaking of amniotic fluid, and infection. These problems are very uncommon.
  • If CVS is done earlier than the 10th week after your last menstrual period, there may be an increased risk that the baby's jaw and limbs will not grow normally. Ask your healthcare provider about this.
  • CVS may be more difficult to do if you are pregnant with more than 1 baby.
  • You may not be able to have CVS if your uterus is not in the proper position.
  • Sometimes it is not possible to get an accurate result from CVS. In these cases, amniocentesis is usually recommended.

When should I call the healthcare provider?

Call your provider right away if:

  • You have a fever over 100°F (37.8°C).
  • You have contractions of the uterus or other pain.
  • You have heavy bleeding or leaking of fluid from the vagina (more than small amounts of spotting).

Call during office hours if:

  • You have questions about the procedure or its result.
  • You want to make another appointment.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.


HIA File preg5218.htm Release 13/2010

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