Chorionic Villus Sampling (CVS)

What is chorionic villus sampling?

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

CVS is similar to amniocentesis. Amniocentesis is a procedure in which fluid is sampled from the sac surrounding the baby. Amniocentesis is usually done between the 15th and 18th weeks of pregnancy. CVS can be done several weeks earlier than amniocentesis. It 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 for this purpose later in the pregnancy.

When is it used?

You may consider having CVS because:

• You will be 35 or older on the baby's due date.
• You or the baby's father have a family history of chromosomal or genetic problems.
• 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 and muscular dystrophy.

How do I prepare for chorionic villus sampling?

CVS is usually done 10 to 12 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.

If you have a vaginal infection, it should be treated before the test. For this reason, your health care provider will get 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 either:

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

For transcervical test, a thin plastic tube 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 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.

What happens after the procedure?

Avoid strenuous activity for 1 to 2 days after the procedure. 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 a final result within 2 weeks.

What are the benefits of this procedure?

CVS can be done earlier in pregnancy than amniocentesis. Amniocentesis is usually done during the 15th to 18th weeks of pregnancy. With CVS, you can have the results of genetic tests before the 14th week of pregnancy.

If the test finds a chromosome or genetic problem, you and your health care provider can discuss your options for treatment. For example,

• Some birth defects can be treated before the baby is born.
• You may be able to plan your delivery in a center equipped to deal with birth defects.
• You can get help, such as counseling, that will help you prepare for the baby's problems. There are also many support groups for families who have children with birth defects. You may want to talk with them during your pregnancy or after your baby is born.

What are the risks 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. The risk of these problems is rare, about 1% or less.

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 may not grow normally. Ask your health care provider about this.

CVS is riskier and more difficult to do if you are pregnant with more than 1 baby.

Sometimes it is not possible to get an accurate result from CVS. In these cases, amniocentesis is usually recommended.

When should I call the health care provider?

Call your provider right away if:

• You develop 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.