Chorionic villus sampling

Chorionic Villus Sampling (CVS) is a test done during pregnancy. It looks for certain genetic problems with your baby (fetus). The same genes that are in your baby are in the placenta. The placenta is a large organ that forms in your uterus when you are pregnant. It supplies your baby with nutrients and oxygen through the umbilical cord. A small piece of the placenta is taken out and tested.

This test is done when you are 10 to 13 weeks pregnant.

CVS can find genetic conditions, such as Tay-Sachs disease or hemophilia. It can also find Down syndrome.

You may want to have this test because:

• You are concerned about your baby because of your age. As you get older, you have a greater chance of having a baby with a genetic condition.
• You've had a baby with a genetic condition.
• You or your partner has a family history of a genetic condition.
• You had a result from a screening test that was not normal.

Through the belly

There are two ways to do this test. One way is through the belly (transabdominal). The other way is through the cervix (transcervical).

• You will lie on your back on an exam table.
• Your belly will be cleaned with an antiseptic.
• Your doctor will use ultrasound to guide a long, thin needle through your belly and uterus to the placenta. The needle is used to collect a sample of the chorionic villus cells.

Through the cervix

• You will lie on your back on an exam table.
• Your doctor will put a tool with curved sides (speculum) into your vagina.
• Your doctor will use ultrasound to guide a thin tube (catheter) through your cervix to the placenta.

You may be asked to drink a glass of fluid about an hour before the test so that your bladder is full. A full bladder makes it easier to do the test.

You may want to talk to a genetic counselor before or after the test. This person is trained to give you detailed information about the test. The counselor can help you make decisions about testing. The counselor can also help you understand the results of the tests.

You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

The genetic material (chromosomes) of the cell sample is looked at carefully. Normally there are 46 chromosomes in each cell, arranged in 23 pairs. The number and arrangement of the chromosomes in the sample can show if your baby has a genetic disease. Chromosomes also show the sex of your baby.

It may take 1 to 2 weeks to get CVS results.

CVS can find certain problems, but normal results don't guarantee that your baby will be healthy.

In rare cases, the chorionic villus cells may have abnormal genetic material even though the baby's cells are normal. This is called a false-positive result. An abnormal test result may need to be confirmed by amniocentesis.