Chorionic Villous Sampling
Chorionic Villous Sampling (CVS) is a prenatal test done on pregnant women to test for certain types of birth defects, like Down syndrome. The test was first introduced in the United States in 1983 and has since become a routine procedure offered to women receiving prenatal care. The test takes out a sample of the chorionic villi of the placenta in the uterus. This test is usually performed during the 10th to 12th week of pregnancy.
Similar to an amniocentesis, chorionic villous sampling is usually done on pregnant women over the age of 35, women with a previous pregnancy with birth defects or with a family history of genetic disorders. Chorionic villous sampling carries a slightly higher risk of miscarriage than amniocentesis so you should be well informed about the procedure.
How is CVS Performed?
There are two types of CVS that are currently done on pregnant women: transcervical CVS and transabdominal CVS.
First you will undress and be asked to lay down on an examination table and place your feet in stirrups. Your abdomen and vagina will be disinfected and an ultrasound will be used to locate your placenta. A speculum is used to open your vagina and your cervix will be wiped with antiseptic. The physician will insert a catheter (a long, thin tube) through your vagina and cervix to reach the villi of your placenta. Some women have described the feeling as a slight cramp or pinch. After taking a small sample the physician will remove the tube and put the sample in a small dish. For thirty minutes you will lie on your left side while your baby’s heart rate, your pulse, blood pressure and breathing are monitored.
Depending on your anatomy, your doctor may decide to perform a transabdominal CVS. This procedure is recommended for women who have a retroverted uterus. During this procedure, your abdomen is disinfected and, using the ultrasound, the doctor will insert a needle through your abdomen to reach the villi. After retrieving the sample, the doctor will check the fetus’ heartbeat with the ultrasound. Your pulse, blood pressure and breathing and your baby’s heart rate will be monitored for thirty minutes.
After any of these procedures, it is recommended to relax for a few hours. If you have any cramping, bleeding or spotting, contact your doctor immediately. The test results should be ready within one to two weeks.
What the Test Results Mean
With the test results from CVS, your physician will able to tell if your baby has any birth defects. If your baby has congenital adrenal hyperplasia (CAH), a condition that causes abnormal genitals, the doctor will be able to provide prenatal hormone treatment. Therefore your baby will not need surgery at birth. CVS prenatal testing provides you and your partner the information you need to make informed decisions for your child. The test can reveal over 200 disorders including Down syndrome, hemoglobinopathies or Tay-Sachs disease. If it is discovered that your baby has birth defects, you and your partner can go to a genetic counselor for more information.
Risks of CVS
Studies have shown that CVS has a slightly higher chance of causing miscarriage than amniocentesis. The Center for Disease Control and Prevention has estimated that one in 200 women will miscarry with this procedure. The risk for women with a retroverted uterus is higher at five in 100 miscarriages. Also there is a one in 1,700 risk for limb defects in babies. There have been conflicting reports about whether CVS performed either before or after the 10th week of pregnancy will cause limb defects. It is best if the procedure is performed by an experienced doctor and in a facility that provides both transabdominal and transcervical CVS.
Pros of CVS
Some of the advantageous of having CVS performed include:
- CVS can be performed in the doctor’s office
- It is a simple procedure
- Provides information about birth defects to expectant parents
- With genetic counseling, CVS can help you make decisions about your baby.
Cons of CVS
Some of the disadvantages of CVS may be:
- Higher risk of miscarriage than amniocentesis
- Amniotic membrane may rupture
- Risk of uterine infection
- Risk of limb defects
- May cause bleeding
Additionally, this test could cause your blood to mix with your baby’s blood, which could be problematic if you are Rh negative. In this case, you will be given the drug Rh immunoglobin to prevent your body from producing antibodies against your baby’s blood.
CVS is offered to every pregnant woman but you can decline having the test done if you prefer. Discuss with your health care provider and your partner all the pros and cons of the test and how you would be affected by the results before deciding whether to have the test done.