Chorionic Villus Sampling (CVS)
(CVS, Chorionic Villus Biopsy)
What is chorionic villus sampling?
Chorionic villus sampling (CVS) is a prenatal test that involves taking a sample of tissue from the placenta, a structure in the uterus that provides blood and nutrients from the mother to the fetus, to test for chromosomal abnormalities and certain other genetic problems.
The chorionic villi are tiny projections of placental tissue that look like fingers and contain the same genetic material as the fetus. Testing may be available for other genetic defects and disorders depending on the family history and availability of lab testing at the time of the procedure.
CVS is usually performed between the 10th and 12th weeks of pregnancy. Unlike amniocentesis (another type of prenatal test), CVS does not provide information on neural tube defects, such as spina bifida. For this reason, women who undergo CVS also need a follow-up blood test between 16 to 18 weeks of their pregnancy to screen for neural tube defects.
There are two types of CVS procedures:
Transcervical - a catheter is inserted through the cervix into the placenta to obtain the tissue sample
Transabdominal - a needle is inserted through the abdomen and uterus into the placenta to obtain the tissue sample
Another related procedure that may be used to diagnose genetic and chromosomal defects is amniocentesis. Please see this procedure for additional information.
Anatomy of the fetus in utero:
Amniotic sac - a thin-walled sac that surrounds the fetus during pregnancy. The sac is filled with amniotic fluid (liquid made by the fetus) and the amnion (the membrane that covers the fetal side of the placenta), which protects the fetus from injury and helps to regulate the temperature of the fetus.
Anus - the opening at the end of the anal canal
Cervix - the lower part of the uterus that projects into the vagina. Made up of mostly fibrous tissue and muscle, the cervix is circular in shape.
Fetus - an unborn baby from the eighth week after fertilization until birth
Placenta - an organ, shaped like a flat cake that only grows during pregnancy and provides a metabolic interchange between the fetus and mother. (The fetus takes in oxygen, food, and other substances and eliminates carbon dioxide and other wastes.)
Umbilical cord - a rope-like cord connecting the fetus to the placenta. The umbilical cord contains two arteries and a vein, which carry oxygen and nutrients to the fetus and waste products away from the fetus.
Uterine wall - the wall of the uterus
Uterus (Also called the womb.) - the uterus is a hollow, pear-shaped organ located in a woman's lower abdomen, between the bladder and the rectum, that sheds its lining each month during menstruation and in which a fertilized egg (ovum) becomes implanted and the fetus develops
Vagina - the part of the female genitals, behind the bladder and in front of the rectum, that forms a canal extending from the uterus to the vulva
Reasons for the procedure
Chorionic villus sampling may be used for genetic and chromosome testing in the first trimester of pregnancy in the presence of one or more of the following conditions:
Family history or previous child with a genetic disease, or chromosomal or metabolic disorder
Maternal age over 35 years by the pregnancy due date
Risk of a sex-linked genetic disease
Previous ultrasound with questionable or abnormal findings
There may be other reasons for your physician to recommend a chorionic villus sampling.
Risks of the procedure
As with any invasive procedure, complications may occur. Some possible complications may include, but are not limited to, the following:
Cramping, bleeding, or leaking of amniotic fluid
Limb defects in infants, especially in CVS procedures done before 9 weeks (rare)
Patients who are allergic to or sensitive to medications or latex should notify their physician.
Women with twins or other multiples will need sampling from each placenta in order to study each baby.
There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician prior to the procedure.
Certain factors or conditions may interfere with CVS. These factors include, but are not limited to, the following:
Pregnancy earlier than seven weeks or later than 13 weeks
Position of the baby, placenta, amount of amniotic fluid, or mother's anatomy
Vaginal or cervical infection
Samples that are inadequate for testing, or that may contain maternal tissue
Before the procedure
The physician will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
Generally, there is no special restriction on diet or activity prior to chorionic villus sampling.
Notify your physician if you are sensitive to or are allergic to any medications, latex, iodine, tape, and anesthetic agents (local and general).
Notify your physician of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.
Notify your physician if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.
Notify your physician if you are Rh negative. During the CVS procedure, blood cells from the mother and fetus can mix. This may lead to Rh sensitization and breaking down of fetal red blood cells.
You may or may not be asked to have a full bladder right before the procedure. Depending on the position of the uterus and placenta, a full or empty bladder may help move the uterus into a better position for the procedure.
Based upon your medical condition, your physician may request other specific preparation.
During the procedure
A CVS procedure may be performed on an outpatient basis, or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician’s practices.
Generally, a CVS procedure follows this process:
You will be asked to undress completely, or from the waist down, and put on a hospital gown.
You will be asked to lie down on an examination table and place your hands behind your head.
Your vital signs (blood pressure, heart rate, and breathing rate) will be checked.
An ultrasound will be performed to check the fetal heart rate, and the position of the placenta, fetus, and umbilical cord.
Based on the location of the placenta, the CVS procedure will be performed through your cervix (transcervical) or through your abdominal wall (transabdominal).
For a transcervical CVS procedure:
The physician will insert an instrument called a speculum into your vagina to spread the walls of the vagina apart.
Your vagina and cervix will be cleansed with an antiseptic solution.
Using ultrasound, a thin tube will be guided through the cervix to the chorionic villi.
Cells will be gently suctioned through the tube into a syringe. You may feel a twinge or slight cramping. More than one sample may be needed to obtain enough tissue for testing.
The tube will then be removed.
For a transabdominal CVS procedure:
For an abdominal CVS, your abdomen will be cleansed with an antiseptic. You will be instructed not to touch the sterile area on your abdomen during the procedure.
The physician may inject a local anesthetic to numb the skin. If a local anesthetic is used, you will feel a needle stick when the anesthetic is injected. This may cause a brief stinging sensation.
Ultrasound will be used to help guide a long, thin, hollow needle through your abdomen and into the uterus and placenta. This may be slightly painful, and you may feel a cramp as the needle enters the uterus.
Cells will be gently suctioned into a syringe. More than one sample may be needed to obtain enough tissue for testing.
The needle will then be removed. An adhesive bandage will be placed over the abdominal needle insertion site.
Procedure completion, both methods:
The fetus’ heart rate and your vital signs will be reassessed.
If you are Rh negative, you may be given Rhogam. This is a specially developed blood product that can prevent an Rh negative mother's antibodies from reacting to Rh positive fetal cells.
The chorionic villus tissue will be sent to the lab.
After the procedure
You and your fetus will be monitored for a time after the procedure. Your vital signs and the fetal heart rate will be checked periodically for an hour or longer.
The CVS tissue will be sent to a specialty genetics lab for analysis. Counseling with a genetics specialist may be recommended depending on the test results.
You may experience some slight cramping and light spotting for a few hours after CVS.
You should rest at home and avoid strenuous activities for at least 24 hours. You should not douche or have sexual intercourse for two weeks, or until directed by your physician.
Notify your physician to report any of the following:
If a transabdominal procedure was performed, check the bandaged needle site on your abdomen for any bleeding or drainage of fluid.
Your physician may give you additional or alternate instructions after the procedure, depending on your particular situation.