Sampling of chorionic villus
What is this test?
This test studies a sample of chorionic villus, which is a part of the placenta (the organ that nourishes the baby during pregnancy). This test is used to identify certain birth defects of the unborn baby. This test is done during the first 3 months of pregnancy.
What are other names for this test?
- CVB - Chorionic villus biopsy
- CVS - Chorionic villus sampling
Why do I need this test?
Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. The following is a possible reason why this test may be done:
When and how often should I have this test?
When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.
Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.
The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.
How should I get ready for the test?
CVS is a procedure that requires your written consent. Review the consent form with the healthcare worker and ask any questions that you have before signing the consent form. Tell the person doing the CVS if you have a history of pregnancy difficulties, such as premature (early) labor, incompetent cervix (a weak or failing cervix), placenta previa (a placenta that is abnormally low, near or over the cervix), abruption placentae (the placenta is separate from the uterine wall too early), and if you are Rh negative (Rh incompatibilities happen when a baby’s blood has a protein that the mother does not, thus causing an immune reaction). Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. You should also report if you have a history of allergic or other reactions to local anesthetics. Depending on method used to do the CVS, you may be asked to drink extra fluids and have a full bladder for the procedure.
How is the test done?
The chorionic villus is a part of the placenta (the organ that nourishes the baby during pregnancy). A sample of chorionic villus is collected by a procedure called chorionic villus sampling (CVS). Depending on the location of your placenta, CVS may be done either through your cervix (transcervically) or abdomen (transabdominally). Both methods will require you to lie down and will use ultrasound to assist the sample collection. For a transcervical CVS, you will be in a position similar to a Pap smear. A speculum will be used to gently spread apart your vagina. Your cervix or vagina will be cleaned with an antiseptic solution. A flexible catheter will be placed through your cervix and a small sample removed. For the transabdominal method, a needle will be used to go through the abdominal wall into the placenta. This will allow a syringe to draw out a small sample of placenta.
If a transabdominal method is used, you will be asked to lie on your back. An area of skin on your abdomen will be cleaned with an antiseptic solution, and a sterile area prepared. You will be given anesthetic to numb your skin. When the area is numb, a needle will be placed through your skin and into the placenta. A small sample of the placenta will be collected and the needle will be withdrawn. All CVS procedures may need to be repeated to collect a sufficient sample size.
How will the test feel?
The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the procedure. Inform the person doing the procedure if you feel that you cannot continue with the procedure.
During a transcervical CVS procedure, you may feel mild cramping in your abdomen or pelvic area. Before a transabdominal or transcervical CVS procedure, a local anesthetic is given to the procedure site to numb the area. You may feel mild discomfort or stinging when the numbing medicine is injected. As the procedure needle or catheter is inserted through the abdomen or cervix, you may feel some discomfort and pressure. You may feel mild cramping in your abdomen and pelvic area during the procedure. The procedure site may be sore for several days.
What should I do after the test?
After all CVS procedures, ultrasound and fetal monitoring may be done immediately after the procedure. If a needle was used, pressure may be held to the site until the bleeding or drainage has stopped. A bandage will be placed over the site if a transabdominal method was used. After all CVS procedures, rest is necessary. Do not have sexual intercourse, douche, and avoid heavy lifting for at least 24 hours after all the procedures.
Contact your healthcare worker if there is redness, swelling, pus, drainage, or pain at the procedure site if the transabdominal method was used. For all procedure methods, alert your healthcare worker immediately should you develop a fever; bleeding (heavier than light spotting), fluid leakage or discharge from your vagina; or severe abdominal cramping or pain. An ultrasound is usually done 2 to 4 days after the CVS to make sure that the fetus is doing well.
What are the risks?
Placental tissue (chorionic villus): A placental tissue sample is collected by a procedure called chorionic villus sampling (CVS). Depending on where your placenta is located, different methods may be used. CVS risks, depending on the method, include bleeding and infection at the site. If you have a medical condition, or are using a medication or supplement that causes excessive bleeding, you are at a higher risk of bleeding from the puncture site. It is possible that the needle or catheter that is used to collect the tissue will injure the baby. You may develop a fever, an abnormal vaginal discharge, abdominal pain or cramping, or go into labor. If there is a possibility that you and your baby are not Rh compatible, you may need additional treatment to avoid further complications. There is a risk that your baby will not survive the procedure, or may be adversely affected by this procedure. It is possible that the baby’s limbs, fingers, and toes may be affected by this procedure. The chances of these risks vary depending on your health status, how long you have been pregnant before the CVS procedure, and other factors. The person doing this test may need to perform it more than once. Talk with your healthcare worker if you have any concerns about the risks of having CVS.
What are normal results for this test?
Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:
- Negative for chromosomal abnormality
What follow up should I do after this test?
Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.
After a CVS procedure, it may take from 1 to 4 weeks to receive results. There is a possibility that you may need an amniocentesis if the CVS was not successful.
Where can I get more information?
- Philip J, Silver RK, Wilson RD, et al: Late first-trimester invasive prenatal diagnosis: results of an international randomized trial. Obstet Gynecol 2004; 103(6):1164-1173.