Chorionic Villus Sampling (CVS)

Chorionic Villus Sampling (CVS)

What is chorionic villus sampling?

Chorionic villus sampling (CVS) is
a prenatal test. It is done by taking a sample of tissue from the placenta. The sample
is tested for chromosomal abnormalities and some other genetic problems. The placenta is
an organ in the uterus that send blood and nutrients from the mother to the baby.

The chorionic villi are tiny
fingers of placental tissue. They have the same genetic material as the baby. Testing
may be done for other genetic problems. This depends on the family history and the types
of lab testing that are available.

CVS is usually done between the
10th and 12th weeks of pregnancy. CVS does not give information on neural tube defects
or myelomeningocele (also known as spina bifida). For this reason, women who have CVS
also need a follow-up blood test between 16 to 18 weeks of their pregnancy. This test is
to screen for neural tube defects.

There are 2 types of CVS
procedures:

  • Transcervical. A catheter is
    put through the cervix into the placenta to get the tissue sample.

  • Transabdominal. A needle is
    put through the belly and uterus into the placenta to get the tissue sample.

Another test that may be used to
diagnose genetic and chromosomal defects is amniocentesis. This test does give
information on neural tube defects.

Anatomy of the baby in the
uterus


Illustration of fetus in utero

  • Amniotic sac. This is a
    thin-walled sac that surrounds the baby during pregnancy. The sac is filled
    with amniotic fluid. This is liquid made by the fetus. The sac also contains
    the amnion. This is the membrane that covers the fetal side of the placenta.
    This protects the baby from injury and helps to control the temperature of the
    baby.

  • Anus. This is the opening
    at the end of the anal canal.

  • Cervix. This is the lower
    part of the uterus that dips down into the vagina. It is made of mostly fibrous
    tissue and muscle. It has a circular shape.

  • Fetus. This is a term used
    to describe an unborn baby from the 8th week after fertilization until
    birth.

  • Placenta. This is a flat
    organ inside the uterus that only grows during pregnancy. It sends nutrients
    and other substances between the baby and mother. The placenta allows the baby
    to take in oxygen, food, and other substances. And it lets the baby get rid of
    carbon dioxide and other wastes.

  • Umbilical cord. This is a
    rope-like cord that connects the baby to the placenta. The umbilical cord has 2
    arteries and a vein. They carry oxygen and nutrients to the baby and waste
    products away from the baby.

  • Uterine wall.  This is the
    wall of the uterus.

  • Uterus (also called the
    womb).
     This is a hollow, pear-shaped organ in a woman’s lower belly. It
    sits between the bladder and the rectum. It sheds its lining each month during
    menstruation. When a fertilized egg (ovum) becomes implanted in the lining, a
    baby grows.

  • Vagina. This is a
    canal behind the bladder and in front of the rectum. It forms a path 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. Reasons
that a woman might elect to have CVS include:

  • A previous child with, or
    family history of, a genetic disease, chromosomal abnormalities, or metabolic
    disorder

  • Maternal age over 35 years by
    the pregnancy due date

  • Risk of a sex-linked genetic
    disease

  • Previous ultrasound with
    abnormal results

  • Abnormal cell-free DNA
    test

There may be other reasons for your
healthcare provider to advise a chorionic villus sampling.

Risks of the procedure

All procedures have some risks.
Some risks of this procedure include:

  • Cramping, bleeding, or
    leaking of amniotic fluid (water breaking)

  • Infection

  • Miscarriage

  • Preterm labor

  • Limb defects in infants, a
    higher risk in CVS done before 9 weeks (rare)

People who are allergic to or
sensitive to medicines or latex should tell their healthcare provider.

Women with twins or other multiples
will need sampling from each placenta in order to study each baby.

There may be other risks depending
on your overall health. Talk about any concerns with your healthcare provider before the
procedure.

Certain factors or conditions may
interfere with CVS. These factors include, but are not limited to:

  • Pregnancy earlier than 7
    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 healthcare provider will
    explain the procedure to you. Ask any questions that you have about the
    procedure.

  • You will be asked to sign a
    consent form. This gives your healthcare provider permission to do the procedure.
    Read the form carefully. Ask questions if anything is not clear.

  • There is usually no special
    restriction on diet or activity before CVS.

  • Tell your healthcare provider
    if you are sensitive to or are allergic to any medicines, latex, iodine, tape, and
    anesthetic medicines (local and general).

  • Tell your healthcare provider
    of all medicines (prescribed and over-the-counter) and herbal supplements that you
    are taking.

  • Tell your healthcare provider
    if you have a history of bleeding disorders. Tell him or her if you are taking any
    anticoagulant (blood-thinning) medicines, aspirin, or any other medicines that may
    affect blood clotting. You may need to stop these medicines before the
    procedure.

  • Tell your healthcare provider
    if you are Rh negative. During CVS, blood cells from the mother and baby can mix.
    This may lead to Rh sensitization and breaking down of the baby’s red blood cells.
    In most cases, prenatal blood tests will have already shown if you are Rh
    negative. You may be asked to provide these test results before the procedure.

  • 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 on your medical
    condition, your healthcare provider may request other specific preparation.

During the procedure


Illustration demonstrating a transcervical chorionic villus sampling

A CVS procedure may be done on an
outpatient basis, or as part of your stay in a hospital. Procedures may vary depending
on your condition and your healthcare provider’s practices.

Generally, a CVS procedure follows
this process:

  1. You will be asked to undress
    completely, or from the waist down, and put on a hospital gown.

  2. You will be asked to lie down
    on an exam table.

  3. Your vital signs (blood
    pressure, heart rate, and breathing rate) will be checked.

  4. An ultrasound will be
    performed to check the baby’s heart rate, and the position of the placenta, baby,
    and umbilical cord.

  5. 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:

  1. The healthcare provider
    will put a tool called a speculum into your vagina so that he or she can see
    your cervix.

  2. Your vagina and cervix
    will be cleansed with an antiseptic solution.

  3. Using ultrasound guidance,
    a thin tube will be guided through the cervix to the chorionic villi.

  4. Cells will be gently
    suctioned through the tube into a syringe. You may feel a twinge or slight
    cramping. More than 1 sample may be needed to obtain enough tissue for
    testing.

  5. The tube will then be
    removed.

For a transabdominal CVS
procedure:

  1. For an abdominal CVS, your
    belly will be cleansed with an antiseptic. You will be instructed not to touch
    the sterile area on your belly during the procedure.

  2. The healthcare provider
    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 feeling.

  3. Ultrasound will be used to
    help guide a long, thin, hollow needle through your belly and into the uterus
    and placenta. This may be slightly painful, and you may feel a cramp as the
    needle enters the uterus.

  4. Cells will be gently
    suctioned into a syringe. More than 1 sample may be needed to obtain enough
    tissue for testing.

  5. The needle will then be
    removed. An adhesive bandage will be placed over the abdominal needle insertion
    site.

At the end of either
method:

  1. The baby’s heart rate and
    your vital signs will be checked.

  2. If you are Rh negative,
    you may be given Rho(D) immune globulin. This is a special blood product that
    can prevent an Rh negative mother’s antibodies from reacting to Rh positive
    fetal cells.

  3. The chorionic villus
    tissue will be sent to a lab.

After the procedure

You and your baby will be monitored
for a while after the procedure. Your vital signs and the baby’s heart rate will be
checked periodically for an hour or longer.

The CVS tissue will be sent to a
genetics lab for analysis. Counseling with a genetics specialist may be advised
depending on the test results.

You may have some slight cramping
and light spotting for a few hours after CVS.

You should rest at home. Don’t do
strenuous activities for at least 24 hours. You should not douche or have sexual
intercourse for 2 weeks, or until your healthcare provider says it’s okay.

Call your healthcare provider if
you have any of these:

  • Any bleeding or leaking of
    amniotic fluid from the needle puncture site or the vagina

  • Fever or chills

  • Severe abdominal pain or
    cramping

If a transabdominal procedure was
done, check the bandaged needle site on your belly for any bleeding or leaking of other
fluid.

Your healthcare provider may give
you other instructions after the procedure.