Chorionic Villus Sampling for Prenatal Diagnosis
What is Chorionic Villus Sampling (CVS)?
CVS is an accepted and proven method of prenatal diagnosis. During the CVS test, a small sample of cells (called chorionic villi) is taken from the placenta where it attaches to the wall of the uterus. Chorionic villi are tiny parts of the placenta that are formed from the fertilized egg, so they have the same genes as the fetus.
If you have certain risk factors, you may be offered CVS as a way to detect birth defects during early pregnancy. Whether you choose to have the test is up to you.
How is the test performed?
CVS requires appropriate genetic counseling, including a detailed discussion regarding the risks and benefits of the procedure.
At the time of initial consultation and counseling, an ultrasound exam will be performed to confirm gestational age (the development stage of the embryo) and the location of the placenta. This is done so that CVS can be performed at the appropriate gestational age (which is usually 10-12 weeks from the woman's last menstrual period).
There are two ways to collect chorionic villi from the placenta: through the vagina or through the abdomen.
- To collect cells through the vagina, a speculum is inserted (in the same way as a Pap test). Then a very thin, plastic tube is inserted up the vagina and into the cervix. With ultrasound, the tube is guided up to the placenta, where a small sample is removed.
- To collect cells through the abdomen, a slender needle is inserted through the woman's abdomen to the placenta, much like amniocentesis.
The sample of chorionic villi is then sent to a lab where the cells are grown in a special fluid and tested a few days later. Culture results will be available within 7-10 days. Your physician will directly notify you of the results.
What diseases or disorders can CVS identify?
CVS can help identify chromosomal problems such as Down syndrome or other genetic diseases such as cystic fibrosis, Tay-Sachs disease and sickle cell disease. Since the procedure also identifies the sex of the fetus, it can help identify disorders that are linked to one sex (such as certain types of muscular dystrophy which occur most often in males). CVS does not detect open neural tube defects. If you have CVS, you may want to consider having a blood AFP test later in pregnancy to screen for neural tube defects.
What are the benefits of CVS?
CVS can be done earlier in pregnancy than amniocentesis, and results are usually obtained within 10 days. Getting this kind of information early allows a woman to make choices in the beginning stage of her pregnancy. If a woman chooses to terminate the pregnancy after receiving abnormal test results, the pregnancy termination will be safer than if she waits for amniocentesis results.
What are the potential complications of CVS?
CVS may carry a slightly higher risk of miscarriage than amniocentesis, since the procedure is done in early pregnancy. Infection may also be a complication. Rare cases of limb deformities in infants have been reported, especially when CVS was done before 9 weeks.
Who should be tested?
Your physician can tell you about your risk of birth defects and the tests that are available. Each pregnancy is different, and some risk may be involved. Only you and your partner can decide whether or not you should have this test. Testing should be offered to:
- Pregnant women who will be 35 or older on their due date (the risk of having a baby with a chromosomal problem such as Down syndrome increases with the age of the woman).
- Couples who already have had a child with a birth defect or have a family history of certain birth defects.
- Pregnant women with other abnormal genetic test results.
Amniocentesis: a procedure in which a small amount of amniotic fluid is taken from the sac surrounding the fetus and then tested.
Amniotic fluid: the water in the sac surrounding the fetus in the mother's uterus.
Chorionic villi: microscopic, finger-like projections that make up the placenta.
Chromosomes: structures located inside each cell in the body containing the genes which determine a person's physical make-up.
Embryo: a term that describes the developing baby from the moment of conception to the end of the eighth week of pregnancy.
Fetus: a term that describes the developing baby from the end of the eighth week after conception to the moment of birth.
Placenta: Tissue that connects the woman and fetus. It provides nourishment to the fetus and takes away wastes from the fetus.
Ultrasound: A test in which sound waves are used to examine internal structures. During pregnancy, it can be used to examine the fetus.
Uterus: A muscular organ that is located in the female abdomen and contains and nourishes the developing embryo and fetus during pregnancy.
Information adapted from "Amniocentesis and Chorionic Villus Sampling" by The American College of Obstetrics and Gynecologists
This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. For additional written health information, please contact the Health Information Center at the Cleveland Clinic (216) 444-3771 or toll-free (800) 223-2273 extension 43771 or visit www.clevelandclinic.org/health This document was last reviewed on: 9/9/2002