What is chorionic villus sampling (CVS)?
CVS is a test carried out during pregnancy, which involves removing tissue from the placenta. CVS is used to detect chromosomal abnormalities such as Down syndrome. It can also detect certain other genetic conditions, such as sickle cell disease or thalassaemia major, if your doctor has asked for you to be tested for these.
CVS is also known as a diagnostic test because it gives you a diagnosis. For example, it tells you that your baby does or does not have Down syndrome.
When should the test be carried out?
If you choose to have CVS, it will usually be carried out between the 11th and 14th week of your pregnancy. Occassionally it is carried out later.
Why am I offered the test?
We will offer you an CVS if you have received a HIGH- RISK (Screen Positive) from a screening test for Down syndrome.
You may also be offered a test if:
- doctor thinks you or your baby’s father may have a higher risk of passing on an inherited abnormality to your baby, for example sickle cell disease or thalassaemia major
- you have had a previous pregnancy where your baby was born with a genetic or chromosomal abnormality
- You or people in your family have been born with abnormalities
- You will also be offered this test if your scan has shown that your baby has an increased chance of having a chromosomal or genetic disorder.
Not all women are offered this test.
How do I decide whether I want to have the test?
It can be difficult to make a decision about having an invasive test. You may find it helpful to talk to your doctor, your friends and family. You may also find it helpful to talk to an emotional counselor at BFMC.
You should remember that only you can decide whether or not you want to have this test.
Is there a risk to my pregnancy if I have the test?
An invasive test may increase the risk of you having a miscarriage.
The overall risk of you having a miscarriage after CVS is about 1:200(BFMC outcomes data base). In other words, about one in every 200 women who have a CVS will miscarry.
Can I do anything to prevent a miscarriage after I have had CVS?
There is nothing you can do to prevent a miscarriage after a CVS.
You do not need to rest in bed.It is also hard to tell when you are most likely to miscarry after you have had a CVS. Most miscarriages happen up to two weeks after the test while the risk may last for a total of 4 weeks. Some miscarriages, due to a pregnancy complication, not related to an invasive test will happen anyway, whether the test is done or not, especially when they happen a month after the procedure.
Other screening test results your doctor might need to know about
If your blood group is rhesus negative you will be offered an anti-D injection after the procedure. Your doctor will discuss this with you.
Because CVS is an invasive test, we would want to know whether or not you have HIV or Hepatitis B.
Eating and drinking
It is safe to eat and drink as normal before and after the test.
How is CVS done?
An hour before the test, you will receive a test dose followed by a full dose of an antibiotic (One dose only) to cover infections.
Immediately before the test, your abdomen is cleaned to make sure that the test can take place in the most sterile conditions possible.
During the CVS you will have an ultrasound scan to check the position of your baby. A fine needle is then inserted through your skin, through your abdomen and into your womb. A tiny sample of tissue is then removed from your placenta (your placenta contains tissue that is genetically identical to your baby). The needle does not enter the sac (or bag of fluid) around the baby and so will not touch your baby even if she or he moves during the test.
The test itself takes around 3-5 minutes. Your appointment time may be longer to allow time to discuss the procedure beforehand and because you may need time to rest afterwards (may take half a day).
CVS are almost always done through your abdomen. This is called `transabdominal CVS´.
Is CVS painful?
Most women say that having CVS is uncomfortable rather than painful. Some say it feels like period pain. Women also say they feel anxious before and after the test. You may notice some cramping for a few hours afterwards. This is normal.
You can take paracetamol for any discomfort (remember, you can only take a maximum of eight tablets in 24 hours). If you are worried about taking painkillers or have any questions, you should talk to your doctor or check with us.
If you experience any unusual symptoms immediately after the test or over the next few days (for example, if you have been feeling shivery (as if you have flu), have lost any of the fluid that surrounds your unborn baby (called amniotic fluid), have been bleeding or have contractions), you should call us or your doctor (or both) straight away.
What happens after CVS?
After the test, the sample of the placental tissue will be taken by you to the Genetics laboratory, Manipal Hospital for testing. The tissue sample contains some of your baby’s cells. Cells contain a person’s genetic information. A full karyotype test checks all your baby’s chromosomes. Results from this test are usually ready within two to three weeks.
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