Chorionic villus sampling

Alternative names:

chorionic villus biopsy; CVS

How the test is performed:

The sample is obtained by inserting a catheter through the cervix and into the uterus.

An abdominal ultrasound is taken to determine the position of the uterus, the size of the gestational sack, and the position of the placenta within the uterus. Next you will be placed in the lithotomy position (on your back with knees and legs pulled towards your chest). Your vulva, vagina, and cervix are then cleansed with Betadine. This is done to decrease the possibility of contamination. Finally, a catheter or endoscope is inserted through the cervix, and a sample is taken from the outside of the gestational sack by suction. The sample is then placed in a sample dish and evaluated in the laboratory.

How to prepare for the test:

Your health care provider will explain the procedure and its risks. The morning of the procedure you will be asked to drink fluids and refrain from urinating to FILL your bladder. This can aid in the proper positioning of the uterus, so the sample may be taken. You will be asked to sign a consent form before this procedure, and you may be asked to wear a hospital gown.

How the test will feel:

The ultrasound is not uncomfortable. Jelly is placed on your abdomen, which may be cold, to aid in the quality of the image. Then an instrument is moved to different positions while your health care provider watches the output on a monitor. In addition, your health care provider may apply pressure on your abdomen in an attempt to manually locate the position of your uterus.

The Betadine cleansing solution will feel cold initially, and may irritate your skin if it is not removed after the procedure. Some people are allergic to Betadine. Notify your health care provider if you are allergic to Betadine, or if you have any other allergies.

Patients report that the actual sampling feels similar to a pap smear, where there is some discomfort and a feeling of pressure. There may be a small amount of bleeding following the procedure.

An obstetrician can perform this procedure in about 5 minutes after the preparation.

Why the test is performed:

This test is performed as an early detection tool of congenital defects. The sample is used to study the DNA, chromosomes, and enzymes of the fetus; and can be done before amniocentesis, about 9 to 12 weeks after a missed period.

This test does not detect neural tube defects, and in this capacity will not replace the amniocentesis, but an amniocentesis is not performed until at least 16 weeks into the pregnancy, whereas CVS is done at 8 to 12 weeks. Test results from a CVS are obtained within 1 to 2 weeks, whereas amniocentesis results may take as long as a month. Early diagnosis of congenital defects may relieve some of the concerns of your family, especially if a therapeutic abortion is under consideration. If neural tube defects, Rh incompatibility, or pulmonary maturity are a concern, an amniocentesis will be performed.