Everything you need to know about Chorionic Villous Sampling (CVS)
Chorionic Villous Sampling (CVS) is a diagnostic procedure performed during pregnancy. It helps to obtain a tiny sample of the placenta (afterbirth), which in turn is used for the diagnosis of certain genetic conditions.
Why should I have a Chorionic Villus Sampling CVS?
Chorionic Villus Sampling CVS is not a routine test. Your Doctor may offer you a Chorionic Villus Sampling CVS if there are concerns about specific genetic conditions. The following are typical examples;
1. The most widely known genetic problem is Down’s syndrome. Several screening tests are available to help the parents and doctors determine the risk of a pregnancy being affected before deciding for a CVS.
2. In some cases, the test is done to exclude known genetic problems that run in the family.
3. Routine ultrasound scans on occasions pick up certain features of the baby associated with genetic conditions.
4. Some parents want to be sure that their baby is not affected by a specific disorder.
How is a Chorionic Villus Sampling CVS done?
The procedure is usually done between week 11-14 of your pregnancy. The Doctor will thoroughly explain the procedure to you and get to sign informed consent.
He will check your blood group, your HIV and HepB status. If you are Rh-Negative, you will need an injection of Anti-D after the procedure. If you are HIV or Hep-B positive, having the procedure may increase the risk of passing the infection to the baby.
Usually, the Doctor will perform before the Chorionic Villus Sampling CVS an ultrasound scan to examine the baby and identify the best window for the procedure.
The Doctor will then clean your tummy with an antiseptic solution. A small amount of local anaesthetic will be used to numb the skin where the needle is to be inserted. A thin needle is used for the local anaesthetic; you might find this a bit uncomfortable.
Following the local anaesthetic and under direct ultrasound guidance, the Doctor will pass a fine needle through your tummy into your womb and the afterbirth (placenta). The Doctor’s assistant using a syringe will obtain a tiny sample. It takes a few seconds to take the sample. At the end of the procedure the Doctor will remove the needle.
Most women find the whole procedure uncomfortable rather than painful. On occasions, you might experience mild period-like pains. This not uncommon and simple paracetamol is very helpful.
Rarely, not enough sample is obtained with the first attempt. In this case, the Doctor may have to reinsert the sampling needle.
What information will I get from a Chorionic Villus Sampling CVS?
This will depend on why the test was performed.
In the majority of cases, the aim is to examine the baby’s karyotype (genetic information).
The sample taken contains cells from the placenta. Although the placenta is a separate organ from the baby, it has the same genetic information. The cells obtained can be cultured in the lab. After they are cultured to increase their number and get most of them to start multiplying, using special techniques, the geneticist will look at these cells under the microscope. The karyotype is a snapshot of the baby’s chromosomes. The geneticist will count their number (they should be 46) and examine their morphology (how they look). Usually, due to the time, it takes to culture the cells, this test is ready in 14 days from when it reaches the lab. Some more specialized genetic tests need to be performed; it might take longer. The Doctor should be able to let you know of the approximate time before the test is done.
Rapid tests that only look at certain chromosomes in a small number of cell s (FISH- PCR) are available. These tests usually take 48h after the fluid reaches the lab. Our advice to all is to have the full karyotype in addition to the rapid tests. These tests in the vast majority of cases will give a definitive answer whether the baby is affected or not from the disorder you were testing for
Please note the following;
• The Chorionic Villus Sampling CVS will provide a result for a specific condition. It does NOT guarantee that the baby does not have other genetic disorders.
• Rarely while the Chorionic Villus Sampling CVS was performed to exclude one problem, it picks up another unexpected one. Your Doctor will help you to understand the results and their implications for your baby.
• Rarely (less than 1/100) the Chorionic Villus Sampling CVS may not give a clear a result. A repeat test may be necessary.
What are the risks for my pregnancy?
Unfortunately, a Chorionic Villus Sampling CVS is not without risks. It is generally quoted that there is a risk of 1-2% to have a miscarriage as a result of the test.
In a small number of cases (1:1000), a serious infection might develop.
You should carefully consider these risks against the value of the information you seek to get from the test.
How will I get my results?
Our Doctor or our specialist midwife will call you to let you know of your results. You will also receive a hard copy of the report for your records.
What if my results are abnormal?
Although in most of the cases, the results will come back as normal, there will be those that are going to be affected by the condition we were testing for. Your Doctor will call you to let you know that the results are not normal and ask you to come to the clinic and explain to you the results and what they mean for your pregnancy and your baby. This is a stressful experience, and you might find it helpful to have your partner with you.
We hope you will find this information useful. If you have any questions, you can contact our clinic for a consultation with one of our Fetal Medicine Specialists.