What is chorionic villus sampling (CVS)?

With CVS the tissue which form the placenta, is obtained by placing a needle into the placenta.

The chorionic villus cells originate from the baby, and can be used to diagnose specific conditions of the baby.

Why would a CVS be done?

An CVS is usually done to confirm or exclude possible abnormalities of the fetus (unborn baby). It is most commonly done because of an abnormal screening examination (first trimester ultrasound an blood test), or because of abnormal findings found at the structural ultrasound examination.  Other reasons include advanced maternal age (35 years or older at the time of delivery) or a known genetic abnormality in the family.

Are CVS and amniocentesis similar tests?

Both a CVS and an amniocentesis is used to diagnose conditions such as Down syndrome or genetic abnormalities in the unborn baby.  However, there are some important differences:

  • CVS is done earlier in pregnancy (typically at 11 – 12 weeks) than amniocentesis (typically at 16 – 18 weeks), and the results are therefore available earlier.
  • The risk of causing a miscarriage is similar to that of an amniocentesis (i.e. 1/200).
  • A disadvantage of CVS is that a chromosomal abnormality could be found in the chorionic villi which do not occur in the baby itself.
  • CVS also does not give any indication of the baby’s risk of a spina bifida.
  • There is a larger risk of “non-informative” results with CVS (2%), which could mean that an amniocentesis might be needed even though you have had a CVS.

Who decides whether a CVS should be done or not?

Your doctor or genetic counselor will explain to you why a CVS is offered.  It remains your own choice whether you would like to have this procedure performed or not.

When is a CVS done?

Because the chances for complications are higher if the CVS is done too early, a CVS is done between 11 and 12 weeks of gestation.

Where is a CVS done?

The CVS is done in the consulting rooms, where an ultrasound is present.

How is a CVS done?

Under ultrasound guidance, a thin needle is placed through your abdominal wall into the placenta.  and a sample is obtained. A second sample  might need to be taken by re-inserting the needle. Local anaesthetic may be used. After the needle is removed, the baby’s heart action is shown to you by ultrasound for reassurance.

If your blood group is rhesus negative, and the baby’s father is rhesus positive, you will receive an injection to prevent antibodies developing against the rhesus blood group.

What are the risks associated with a CVS?

  • The risk of miscarriage due to CVS is about 1/200 and this is the same as the risk from amniocentesis at 16 weeks.  Symptoms of this include a cramping abdominal pain, worse than menstrual pains, as well as vaginal bleeding.  If you notice any of these symptoms, please contact your doctor immediately.
  • An infection could develop in the womb.  Symptoms of this are fever, cold shakes, a constant pain over the womb, and sometimes an offensive vaginal discharge. If you notice any of these symptoms, please contact your doctor immediately.
  • Some studies have shown that when CVS is performed before 10 weeks there is a small risk of abnormality in the baby’s fingers and/or toes. To avoid this risk we never perform CVS before 11 weeks.

When will the results be available?

Provisional results are available in less than one week, and the final results should be available after three weeks.  We can contact you by telephone as soon as the result is available if you prefer.  A copy of the result is also forwarded immediately to your gynaecologist.

What are the alternatives to CVS?

  • Screening tests such as an ultrasound examination (preferably between 11 and 13 weeks of gestation) and /or a blood test can give you a accurate estimate of your risk of having a baby with Down syndrome or other chromosomal abnormalities.  If the risk is low, according to one or both of these tests, you might decide against an amniocentesis.  Invasive tests (e.g. amniocentesis, cordocentesis or chorionic villus biopsy) is the only definite way currently available to exclude a chromosomal abnormality.
  • Cell-free fetal DNA tests are non-invasive, and test for genetic conditions in the baby by extracting its DNA from a blood sample of the mother. These tests are very accurate, but not quite as conclusive as invasive tests, and are still expensive.

  •  Other invasive tests include amniocentesis and cordocentesis.
    • Amniocentesis is the most commonly performed invasive test. For further information, please see the information on amniocentesis.
    • Cordocentesis entails obtaining a blood specimen from the baby’s umbilical cord.  It is usually only done after 20 weeks of gestation.  There is approximately a 1% risk of miscarriage, but it has the advantage that a full result is available within a few days.  It is usually done where a physical anomaly of the baby is found on ultrasound, or where there has been a delay in doing an amniocentesis.

Which results can I expect from the CVS?

  • The chromosome results should exclude or confirm the possibility of Down syndrome and other chromosomal abnormalities.
  • It also indicates the baby’s gender.  (Please indicate whether you would like to know this!)
  • Rarely, the following could happen:
    • A so-called chromosomal “mosaic” could be found.  This means that some cells are normal, and others abnormal.  It sometimes reflects the baby’s chromosomal make-up, but can also be due an effect of  the cell culture, or be restricted to the placenta, with normal fetal chromosomes.  If a mosaic is found, it could be necessary to do an amniocentesis.
    • Chromosomal abnormalities of uncertain importance, could be found.  This includes findings such as:
    • A translocation, where part of one chromosome is found in another chromosome.  This might have implications for the baby once he/she has grown up, and has children of his/her own.
    • Fractured chromosomes, where the chromosome breaks up in the cell culture.  This might have health implications for the baby as an adult.
    • Extra X-chromosomes. This might have implications for the baby once he/she has grown up, and has children of his/her own.
    • The baby’s gender as seen on ultrasound might differ from the gender according to the CVS.  This might mean that the ultrasound is wrong, that an error has slipped in with the reporting of the results of the amniocentesis, or that a real difference exists between the baby’s genetic and physical gender.  It is important to distinguish this difference before the birth!

Which precautions should I take before the CVS?

  • A full bladder is unnecessary for the ultrasound. An empty bladder is less uncomfortable!
  • Bring someone along for moral support.  It is possible to drive home by yourself, but still better if some else does the driving.
  • Let us know if you have any bleeding tendency, or if you are using any medication (including low-dose aspirin or arnica).
  • Arrange to have the rest of the day off work.  (Please let us know if we should send you a note in this regard.)
  • Make sure to which extent your medical aid will refund the CVS – both the CVS itself, and the analyses in the cytogenetical laboratories. Please note that you will receive two separate accounts for the CVS: one by ourselves for the procedure, and one by the laboratory for the cell culture and karyotyping.  The laboratory fee will double for twins, triple for triplets etc.
  • If you are HIV positive, there is a potential risk of transferring the HIVirus to the baby with a CVS.  If you are HIV positive, or would like to be tested for HIV before the cordocentesis, please let us know beforehand.

Which precautions should I take after the CVS?

  • Take the rest of the day off work, and rest at home.  It is not necessary to stay in bed, but do not do any physically strenuous work or exercises.
  • Do not pick up any heavy objects in the next two to three days.  (Including a toddler!)
  • Contact us or your gynaecologist if any of the following should develop:
  • Stomach pains or cramps, worse than with a menstrual period, and which do not improve by using analgaesics. (one or two tablets of paracetamol, e.g. Panado® or Dolorol®)
  • Vaginal bleeding
  • Watery vaginal discharge
  •  Fever or rigors
  • Offensive vaginal discharge

USEFUL LINKS

Chromosomal abnormalities