What is Chorionic Villous Sampling ?
CVS is a prenatal diagnostic test performed in pregnancy. It is used to test for chromosomal abnormalities. It involves passing a needle through the skin of the mother, through the wall of the uterus(womb) and taking a small sample of the Placenta of developing baby. The needle does not touch the baby. The placenta and the baby develop from the same egg and hence have the same genetic material(except in cases of placental mosaicism which is rare).
Who should get CVS done?
It may be recommended if you have an increased risk of having a baby with a birth defect. For example if you have:
1. A genetic disorder
2. A previous child with a genetic disorder
3. A family history of a genetic disorder
4. Any structural defect on ultrasound
You can discuss all of the testing options and your individual risk factors before deciding on whether or not to have the test.
CVS is usually done between 11 and 14 weeks of pregnancy.
How is the procedure done?
You would have to come with your husband/relative for the procedure. Prior to the procedure, you would be explained the procedure with its benefits and risk. You would be asked to sign a written consent.
You may be asked to empty your bladder before the procedure.
Like an ultrasound examination, you would be asked to lie down on a couch. Your tummy would be cleaned by antiseptic. A local anaesthetic injection is used to numb a small area.
A thin needle is inserted through the abdomen (belly) and into the uterus guided by ultrasound.
A small sample of placenta is withdrawn.
The sample is sent to a lab for testing.
After the needle is removed and the baby is checked, you will be able to leave the room. You will need to lie down for 30-60 minutes or so and then you can go home.
Is CVS Painful?
Most women say that CVS is uncomfortable rather than painful. Some say it feels something like period pain. You may feel anxious before and after the test. You may notice some cramping for a few hours afterwards.
Are there any risks?
CVS being an invasive procedure, carries a small(1 in 200) risk of miscarriage, bleeding or leaking from vagina post procedure.
There is a risk of less than 1 in 1,000 that CVS will cause a serious infection.
It is not always possible to get a result from the first CVS. In that case you would be offered a second procedure.
There is a rare condition called confined placental mosaicism (CPM) in which the DNA in the placenta is not the same as the baby’s. In this case, the results will not be reflective of the baby.
When will we get the results?
The results depends on the type test that is done on the sample. It may range from 3days to 1 month. You may also get the results stepwise if multiple tests are requested.
Note :
If your blood group is Rh (rhesus) negative, it will be recommended that you have an injection of anti-D immunoglobulin before the procedure to prevent you from developing antibodies against your baby’s blood cells.
If you have HIV, hepatitis B or hepatitis C viruses, CVS might increase the risk that you pass this on to your baby. You are expected to get screened for these viruses before the procedure. If you screen positive for any of these, your options and further care would be discussed.