Chorionic villous sampling (CVS)
How can I decide whether to have CVS, or not?
CVS stands for chorionic villous sampling and is a medical procedure performed during early pregnancy to take a small sample of tissue from your developing placenta. This sample of tissue will contain the fetal DNA that can be analysed in a laboratory. This is called genetic screening and can help diagnose abnormalities of the unborn baby. Prenatal diagnosis by genetic screening can detect Down’s syndrome, cystic fibrosis and other conditions caused by chromosomal abnormalities. It can also be used for prenatal paternity testing.
The laboratory analyses the tissue sample using a process called PCR (polymerase chain reaction.) It obtains a preliminary result of the testing for Down’s syndrome and a chromosome analysis very quickly. Results from a full analysis for other chromosomal abnormalities can take up to two weeks.
The best time for CVS is around 12 weeks of pregnancy and not after 14 weeks. Before agreeing to the procedure, the risks are explained and you are given time to ask questions you will usually be required to give consent to the procedure; as there is a risk of miscarriage for example. If you'd like to know the gender of your baby, please tell the consultant during your appointment.CVS, however is not solely performed for the purposes of gender identification.
The procedure is usually very straightforward. It is performed under continuous ultrasound vision to avoid any threat to your baby. The consultant will apply some local anaesthetic, before inserting the fine needle. This ensures minimum discomfort and the procedure only takes a minute or two. The doctor draws up a tiny sample of the developing placenta via a syringe into some sterile pink media.
Most of the appointment time is taken up with preparation and counselling. It is important to know your blood group beforehand, for example
In approximately 5% of patients it is not possible to perform CVS due to the position of the placenta. Unfortunately there is nothing that can be done to predict when this might happen, or to avoid it. The only solution is to wait until at least 16 weeks gestation to do an amniocentesis.
Consult your doctor if:
• you have a family history of chromosomal abnormalities
• your nuchal scan and blood testing for Down syndrome indicate a high level of risk
• you wish to have CVS performed for your own peace of mind.
At Richmond Practice prenatal diagnosis such as CVS and amniocentesis are performed as part of our private pregnancy care packages and/or as a stand-alone procedure on a once off basis. The consultants who undertake this procedure are obstetricians who are also sub-specialists in fetal maternal medicine. We take great care to ensure that you will be comfortable during and after the procedure. You will also have the chance to see a 3D picture of your baby and to have a photo of your unborn baby saved in a picture frame.