CVS Test: Use and Risks

CVS stands for Chorionic Villus Sampling, a prenatal test done to detect chromosomal abnormalities or genetic disorders in a fetus, such as Down syndrome. In this test, a doctor takes a sample of cells from the chorionic villi of the placenta to send to the lab for analysis.

Compared to amniocentesis, which also detects genetic abnormalities in women who are at risk for carrying chromosomal problems, CVS offers the advantage of being able to test early in pregnancy (10 to 12 weeks). Amniocentesis is usually done on the 16th week of pregnancy. Both tests involve an invasive procedure, which carries some risk of abortion or miscarriage.

What Problems Does CVS Test Detect?

A CVS test detects chromosomal abnormalities like Down syndrome and other genetic disorders like cystic fibrosis. Unlike amniocentesis, it does not test for defects in the neural tube.

CVS can also be used for paternity testing before delivery of the baby. The potential father's DNA is collected and this is compared to the baby's DNA, which is collected by CVS. The test is 99% accurate in determining paternity.

How to Prepare for a CVS Test

  • Ask someone to accompany you to the doctor's clinic or hospital to provide emotional support and to drive you home after the procedure.
  • Drink plenty of fluids to fill up your bladder in preparation for the procedure. If needed, you may be asked to empty the bladder before testing.
  • Sign a consent form after you have read it thoroughly before undergoing the procedure.

What Happens During a CVS Test?

A CVS test is an outpatient procedure which can be done in a doctor's office.

During the Procedure

An ultrasound device is used to determine the gestational age of your baby as well as the placenta's position in the uterus. You will be asked to lie down on the examining table with your abdomen exposed. A special gel is applied on the abdomen and the ultrasound transducer is used to show the position of the baby, as seen on a monitor. The image will guide the doctor when taking a tissue sample from your placenta.

  • Transcervical CVS. The doctor can take a sample of tissue through your cervix if the placenta is favorably positioned. This is done by inserting a catheter (a thin, hollow tube) into the cervix after inserting a speculum into the vagina to open it. The catheter is placed near the placenta and is used to obtain tissue sampling by gentle suction. You may feel some cramping during the procedure.
  • Transabdominal CVS. This is done if your placenta is not accessible through your cervix or in the presence of cervical infection. The doctor takes the sample using a long, thin needle inserted through the abdomen and uterus. A stinging sensation may be felt on the skin and some cramping when the uterus is reached.

The entire CVS procedure may take about 30 minutes to accomplish. The procedure is repeated if the first try is not successful.

After the Procedure

  • The doctor monitors the baby's heart beats after the procedure. Some vaginal bleeding may follow.
  • You will be asked to wait for the lab results, which can take between a few days to a couple of weeks.
  • Complications may occur after the procedure and you should call your doctor if you experience heavy vaginal bleeding, fever, painful uterine contractions, and vaginal fluid leak.

Understand the Results

Your doctor or genetic counselor will discuss the results with you. If the test results are not clear, an amniocentesis may be needed to ascertain the diagnosis.

A CVS rarely gives a false-positive result, which means that the results are positive, but there is actually no disease or abnormality. However, it cannot identify all types of birth defects, such as spina bifida or other defects of the neural tube.

If the results indicate that there is a chromosomal abnormality that cannot be treated, you might be asked to decide whether you want to continue with your pregnancy. Seek support from your loved ones and from the health care team.

What Are the Risks of CVS Test?

Miscarriage

One out of 100 CVS tests may lead to a miscarriage, which is more likely to occur when CVS is done transcervical rather than transabdominal. Miscarriage is also more likely to occur if the baby is small for gestational age.

Rh sensitization

CVS test  may cause the baby's blood to enter the mother's bloodstream. To prevent a blood reaction if the mother's blood is Rh negative, Rh immunoglobulin is injected to the mother, thus avoiding antibody production.

Infection

Although rare, CVS test may trigger an infection in the uterus.

Defects in the baby

This is possible only when CVS test is done before the 9th week of pregnancy.

How to Decide If You Need a CVS Test or Amniocentesis Test?

Both tests help diagnose a chromosomal problem or some genetic disorder that affects your baby.

  • Time of test. If you want to be sure that there is no problem with your baby's condition as soon as possible, you can choose to have a CVS test, which can be done in the first trimester. However, if you want to wait a little more before being subjected to an invasive procedure, an amniocentesis is more appropriate.
  • Neural tube defect. Another factor to consider is if you want to detect a neural tube defect in the baby, you will have to do an amniocentesis since a CVS test does not diagnose this condition.
  • Risk of miscarriage. In terms of possible complications, a miscarriage is more likely to occur with a CVS test than with an amniocentesis, especially if specialists in your medical center are less experienced with this procedure.

It is best to discuss these matters with your partner first before making a major decision, as well as your doctor and the genetic counselor, if possible. Watch a video to learn more on CVS Prenatal Test: