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CVS Leaflet
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This leaflet has been written to provide you with information about Chorionic Villus Sampling (CVS). This is not a routine test but is offered to test for Down's syndrome, other chromosome disorders or specific genetic conditions.
WHO SHOULD CONSIDER CVS?
The final decision about having any test in pregnancy is yours but the following women may consider CVS:
- Women with a high-risk result for Down's following a nuchal scan, or a nuchal scan combined with a blood test.
- Women who have a potential problem found on the ultrasound scan which may suggest a chromosomal or genetic abnormality.
- Women who have had a pregnancy or a child affected by a genetic condition that can be tested for by CVS
- A couple who have had a baby with a chromosomal abnormality such as Down's syndrome.
- Those who have a family history of genetic disorders including some rare inherited diseases that can be tested for by CVS.
- Women who do not wish to have screening tests but want to know for sure whether their baby has a chromosome problem.
WHAT ARE THE PROBLEMS ASSOCIATED WITH CVS?
CVS has been available mainly in specialist centres since the early 1990s. In Britain thousands of women have the test performed every year, so we know a lot about its safety and accuracy. We know that 1 in every 100 women who have the test will miscarry as a result of the procedure. There is no evidence that the procedure itself harms your baby as the test is carried out under ultrasound guidance.
IS THE CVS RELIABLE?
No test is absolutely perfect, but the chromosome test for Down's syndrome is over 99% reliable. It fails to give a clear result in fewer than 5 in 1000 cases. If you are having the CVS for specific genetic disorders, you should discuss the accuracy of the test with your genetic doctor or counsellor.
WILL THE CVS TELL ME ABOUT ANYTHING OTHER THAN DOWN'S SYNDROME?
Although you may be having an amniocentesis to detect Down's syndrome, the test may occasionally detect problems with the other chromosomes. If the results show anything abnormal you will be told what the abnormality is and how this will affect your baby.
WHEN IS A CVS PERFORMED?
The test is performed from 11 weeks of pregnancy onwards. Occasionally, if the placenta is in an inaccessible position, the procedure may be deferred by one or two weeks.
HOW IS A CVS PERFORMED?
The test involves taking a small amount of cells from the placenta; these are identical to the baby's cells.
Before the test is performed, an ultrasound scan is carried out to check your dates and the position of both the baby and the placenta (afterbirth). You will not need a full bladder for this scan.
The skin over the abdomen is cleaned and a fine needle is then passed into the womb, then into the placenta. A sample of placental cells is removed and sent to the laboratory. The position of the needle is monitored by ultrasound throughout the procedure.
IS A CVS PAINFUL?
Most women say afterwards that the test is uncomfortable rather than painful and feels similar to period pain. Generally women say that the thought of it is worse than the actual test.
WHAT HAPPENS AFTER THE CVS TEST?
You will probably be at the hospital for about half an hour but the test itself only takes a few minutes.
If your blood group is Rhesus negative, you will need to be given an injection following the procedure to prevent the formation of antibodies in your blood, which may affect future pregnancies.
You should not drive immediately after the test, as you may feel uncomfortable. We encourage you to bring a companion with you for support during and after the test. It is a good idea to take things easy for a couple of days afterwards, avoiding any heavy lifting or strenuous exercise.
The period pain feeling may persist for 24-48 hours. This is not unusual and should settle with paracetamol, which is safe to take in pregnancy. If you have excessive pain, are losing fluid or blood vaginally, develop a high temperature, or feel flu-like symptoms, please contact either us or your local labour ward for advice.
WHEN DO YOU GET THE RESULTS?
A rapid (FISH) chromosome result for the major chromosome abnormalities such as Down's, Edward's, Patau's and sex chromosome abnormalities will be available in 72 hours. The full chromosome test involves growing the cells in the laboratory and this usually takes about 10 days.
If the chromosomes are normal, we will send you the result by post.
WHAT IF THE RESULTS ARE ABNORMAL?
If a chromosome problem is detected, your own Consultant will be contacted with the result. You would usually be contacted by telephone and given an opportunity to discuss the findings. You will be told what the abnormality is and how this could affect your baby. You will have the chance to discuss the results fully before making any decisions.
HIV INFECTION
We would encourage women who are HIV positive to discuss this with their specialist midwife or doctor to obtain further information before invasive testing as there is a risk that the HIV virus can be passed to the developing baby during the procedure.
OUTCOME OF PREGNANCY
Outcome information is very important to us as this enables us to audit and improve our service. Following your appointment with us you will be given an outcome form and an addressed envelope, which we would be very grateful if you would complete and return to us.
...AND FINALLY
If you have any questions about amniocentesis please telephone the Cambridge Fetal Care on 01223 217227 or the Fetal Medicine Unit at the Rosie on 01223-216185. We can arrange for a Fetal Medicine midwife to talk to you if you wish.
We recognise that everyone will have his or her own particular questions and concerns to discuss. The midwife will usually be able to answer any questions you may have before you have the test.