Chorionic villus sampling is a prenatal diagnostic test. What can the test reveal? Will it hurt? What are the risks? Get answers to these questions and more.
Definition
Chorionic villus sampling (CVS) is a prenatal test in which a sample of chorionic villi is removed from the placenta for testing.
During pregnancy, the placenta provides oxygen and nutrients to the growing baby and removes waste products from the baby's blood. The chorionic villi are wispy projections that make up most of the placenta and share the baby's genetic makeup.
Chorionic villus sampling can reveal whether a baby has a chromosomal abnormality, such as Down syndrome. Chorionic villus sampling can also be used to test for other genetic disorders, such as Tay-Sachs disease and cystic fibrosis.
Why it's done
Chorionic villus sampling can provide information about your baby's genetic makeup. Generally, chorionic villus sampling is offered when the test results may have a significant impact on the management of the pregnancy — or your desire to continue the pregnancy. Often, the value of this information can only be assessed by you and your partner.
Chorionic villus sampling is usually done between the 10th and 12th weeks of pregnancy — earlier than other prenatal diagnostic tests, such as amniocentesis.
You may consider chorionic villus sampling if:
- You had abnormal results from a prenatal screening test. If the results of a screening test — such as the first trimester screen — are positive or worrisome, you may opt for chorionic villus sampling to confirm or rule out a diagnosis.
- You had a chromosomal abnormality in a previous pregnancy. If a previous pregnancy was affected by Down syndrome or another chromosomal abnormality, this pregnancy is at higher risk, too.
- You're age 35 or older. Babies born to women age 35 and older have a higher risk of chromosomal abnormalities, such as Down syndrome.
- You have a family history of a specific genetic disorder, or you or your partner is a known carrier of a genetic disorder. In addition to identifying Down syndrome, chorionic villus sampling can be used to diagnose many other genetic disorders — such as Tay-Sachs disease and cystic fibrosis. This requires specialized testing of the chorionic villi, however, so there must be a reason to test for these conditions.
Chorionic villus sampling cannot detect neural tube defects, such as spina bifida. If neural tube defects are a concern, an ultrasound or genetic amniocentesis may be recommended instead.
Risks
Chorionic villus sampling carries various risks, including:
- Miscarriage. Overall, chorionic villus sampling has a one in 100 risk of miscarriage. The risk of miscarriage appears to be slightly higher when the tissue sample is taken through the cervix (transcervical) rather than the abdominal wall (transabdominal). The risk of miscarriage also increases if the baby is smaller than normal for his or her gestational age.
- Cramping and vaginal bleeding. You may feel cramping after the test. Vaginal bleeding also is possible, especially if the cell sample was taken through your cervix rather than the abdominal wall.
- Rh sensitization. Chorionic villus sampling may cause some of the baby's blood cells to enter your bloodstream. If you have Rh negative blood, you'll be given a drug called Rh immunoglobulin after the test to prevent you from producing antibodies against your baby's blood cells.
- Infection. Very rarely, chorionic villus sampling may trigger a uterine infection.
Some older studies suggested that chorionic villus sampling may cause defects in a baby's fingers or toes. However, the risk appears to be a concern only if the procedure is done before the ninth week of pregnancy.
Remember, chorionic villus sampling is typically offered when the test results may have a significant impact on the management of the pregnancy. Ultimately, the decision to have chorionic villus sampling is up to you. Your health care provider or genetic counselor can help you weigh all the factors in the decision.
If you develop heavy bleeding or a fever after chorionic villus sampling, contact your health care provider.
How you prepare
Before chorionic villus sampling, you can eat and drink as usual. Your bladder must be full before the procedure, however, so drink plenty of fluids before your appointment. Your health care provider may ask you to sign a consent form before the procedure begins. You may want to ask your partner or another close contact to accompany you to the appointment for emotional support or to drive you home afterward.
What you can expect
Chorionic villus sampling is usually done in an outpatient facility or the health care provider's office.
During the procedure
First, your health care provider will use ultrasound to determine your baby's gestational age and the position of the placenta. You'll lie on your back on an exam table and lift your shirt to expose your abdomen. Your health care provider will apply a special gel to your abdomen, and then use a small device known as an ultrasound transducer to show your baby's position on a monitor.
Next, your health care provider will take the tissue sample from the placenta. This may be done through your cervix (transcervical) or your abdominal wall (transabdominal).
- Transcervical chorionic villus sampling. If the placenta is in a favorable position, your health care provider may take the sample through your cervix. After cleansing your vagina and cervix with an antiseptic, he or she will open your vagina with a speculum and insert a thin, hollow tube (catheter) through your cervix. When the catheter reaches the placenta, gentle suction will be used to remove a small tissue sample. You may feel cramping while the tissue sample is removed.
- Transabdominal chorionic villus sampling. If the placenta isn't clearly accessible through the cervix or you have a cervical infection, such as chlamydia or herpes, your health care provider may take the sample through a needle inserted into your uterus. After cleansing your abdomen with an antiseptic, he or she will insert a long, thin needle through your abdominal wall and into your uterus. You may notice a stinging sensation when the needle enters your skin, and you may feel cramping when the needle enters your uterus. The tissue sample from the placenta will be withdrawn into a syringe, and the needle will be removed.
You'll need to lie still while the tissue sample is removed. The entire procedure usually takes about an hour, although most of that time is devoted to the ultrasound exam. Your baby will naturally replace the small amount of tissue that's removed.
If your health care provider isn't able to remove an adequate amount of tissue on the first try, the procedure may need to be repeated.
After the procedure
After the tissue sample is removed, your health care provider may use ultrasound to monitor your baby's heart rate. You may experience cramping or a small amount of vaginal bleeding immediately after the procedure. Your health care provider may suggest resting for the remainder of the day. You may want to ask someone to drive you home. You'll likely be able to resume normal activities the next day.
Meanwhile, the tissue sample will be analyzed in a lab. Some results may be available within a few days. Other results may take one to two weeks, depending on the complexity of the lab analysis.
Results
Your health care provider or a genetic counselor will help you understand your chorionic villus sampling results.
Most test results are normal, which can ease anxiety about your baby's health. Sometimes a follow-up ultrasound is recommended several days after chorionic villus sampling to verify the baby's well-being. Occasionally, test results are unclear and amniocentesis is needed to clarify the diagnosis.
With chorionic villus sampling, there's a rare chance of a false-positive test — when the test is positive, but no disease exists. It's also important to remember that chorionic villus sampling can't identify all birth defects, including spina bifida and other neural tube defects.
If chorionic villus sampling indicates that your baby has a chromosomal problem or a genetic disorder that can't be treated, you may be faced with wrenching decisions — such as whether to continue the pregnancy. Seek support from your health care team, your loved ones and other close contacts during this difficult time.
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