Chorionic Villus Sampling, CVS (11+ weeks) Including Rapid FISH Result & Full Karyotype
Chorionic villus sampling involves taking a sample of cells from the placenta of a pregnant woman. These cells are called chorionic villi. It is requested when there is heightened concern about Down’s syndrome or other chromosomal conditions either following a nuchal scan, a harmony test, a previous affected baby, or simply for maternal reassurance.
The procedure is always carried out under the continuous guidance of an ultrasound scan to ensure that the needle does not enter the amniotic sac (the protective sac that cushions the baby with fluid as it grows) or touches the baby.
This test carries a small, but important, risk of miscarriage (1%).
How is the test performed?
After discussion with our experienced fetal medicine consultants a scan is performed trans-abdominally by placing a probe on the tummy. Your tummy is then cleansed with antiseptic, you are given a local anaesthetic by injection and a very fine needle is inserted through your skin into the womb.
The needle is guided towards the placenta using the image on the ultrasound scan. Attached to the needle is a syringe, which is used to extract a small sample of chorionic villi. After the sample is removed, the needle is taken out.
The procedure does not take long and women describe the sensation as mild discomfort rather than painful.
Occasionally due to the position of the placenta we are unable to obtain a sample. If it is not safe to proceed with the procedure at the time of your appointment we will book a repeat appointment roughly a week later and see if the womb has changed position (this occurs naturally as the pregnancy progresses) and makes the placenta more accessible.
How to prepare for your test
No preparation is required prior to this test. However we recommend that somebody accompanies you to your appointment.
What does this package include?
An abdominal ultrasound scan to check the position of the fetus and placenta.
- A discussion about the scan findings or the findings of any other relevant medical/obstetric history or testing you may have had in this pregnancy.
- A CVS performed under ultrasound guidance.
- A rapid PCR result (usually available in three working days) providing a result for Down’s syndrome (trisomy 21) and two other common chromosomal conditions Edward’s syndrome and Patau’s Syndrome(trisomies 18 and 13)
- A Full Karyotype (usually available two weeks after your test) providing information on all of the fetus’ chromosomes.
- Telephone follow up with an experienced midwife to discuss all low and high risk results and any question or concerns you may have.
One of the main risks of a CVS test is miscarriage. This is estimated to occur in around 1% of pregnancies nationally after a CVS test.
A CVS test is uncomfortable rather than painful and you may feel slight cramping for a day or two afterwards. Signs to look out for and who to call should you have any concerns after the test will be discussed with you during your consultation.
Occasionally it is necessary to perform a second test as the sample taken at the first doesn't culture in the lab or provides a confusing result. It is not always known why this happens and we cannot predict cases where this will happen.