At a glance
Looking for a more accurate Down Syndrome screening? Want to avoid the risks associated with diagnostic testing like a CVS? Have you considered a Harmony prenatal test?
A CVS is an accurate diagnostic test for specific genetic abnormalities in early pregnancy - normally Down Syndrome, Edwards’ and Patau Syndromes. Other tests can be performed at an additional cost.
- No GP referral required
- Procedure performed by a highly qualified fetal medicine specialist
- Service not available on the NHS for low risk pregnancies
- Appointments available at short notice
- Convenient central London location
You will receive
- Results in 3-6 days
- Two-page clinical report, plus genetic results
- 100% accurate gender identification, if you want to know
What we need to know before
To assist with the procedure you will need written confirmation of your blood group. If you don’t have this we can help you arrange a blood test when you book.
What happens with your results?
We will call you 3-6 days after your appointment to let you know your results.
What is a CVS?
A CVS or Chorion Villus Sampling, is the name give to a medical procedure performed during early pregnancy; it involves taking a small sample of tissue from your developing placenta.
The sample is then analysed in a genetic laboratory to diagnose any genetic abnormalities of your unborn baby.
Because the tissue, known as the villi, will eventually form your placenta, genetic analysis of the sample will give the same results as if the fetus itself were examined.
Why have a CVS?
A CVS is usually offered on the NHS or privately, if you have received a high risk of an abnormality from your first trimester screening, such as the nuchal scan.
You can choose to have a CVS performed for your own peace of mind, regardless if you have received a high or low risk screening result. The choice is up to you.
Looking for a more accurate Down Syndrome screening? Want to avoid the risks associated with diagnostic testing? Have you considered a Non-Invasive Prenatal Test?
What does the CVS test check for?
The sample will be tested for Down Syndrome, Edward’s Syndrome and Patau Syndrome and will be given a chromosomal analysis to detect disorders such as Klinefelter Syndrome. We will also check for Cystic Fibrosis, at no extra charge, if there is a family history of the condition.
Genetic testing can also be performed for other identifiable problems at an additional charge. These supplementary tests can be included if there is a family history or other children have been born with the condition.
A consultation with one of our fetal medicine specialists will be necessary before proceeding with any of the following tests, and in some instances an appointment with a consultant geneticist will be required:
- Smith-Magenis Syndrome
- Miller-Dieker Syndrome
- DiGeorge Syndrome
- Prader-Willi Syndrome
- Angelman Syndrome
- Wolf-Hirschhorm Syndrome
- Cri du Chat Syndrome
- Langer Giedion Syndrome
- Phelan-McDermid Syndrome
- 15q24 Deletion Syndrome
- 17q21.21 Microdeletion Syndrome
- Analysis of subtelomeric regions of all 46 chromosomes
A CVS can also be perfomed to obtain samples for pre-natal paternity testing.
What happens during a CVS appointment?
Most of the appointment time is taken up with preparation and counselling, allowing you time to ask the consultant any questions and to sign a consent form which will be fully explained to you. The actual chorion villus sampling only takes one or two minutes and is usually completed before you realise it.
Taking the sample
During the CVS the consultant will pass a fine needle through your tummy into the placental tissue on the outside of your pregnancy sac. A local anaesthetic is applied before the needle is inserted to ensure there is minimum discomfort. The doctor will draw up a tiny sample of your developing placenta using a syringe.
Although the procedure sounds frightening, in reality it is usually very straightforward and is performed under continuous ultrasound vision to avoid any threat to your baby. Before the procedure we will need confirmation of your blood group, if you are Rhesus Negative we will need to give you an injection of Anti-D once the CVS has been performed. This injection carries an additional charge.
Position of placenta
In 5% of patients we are unable to perform a CVS due to the position of the placenta and/or internal organs. The only solution is to wait until at least 16 weeks gestation when an amniocentesis can be performed.
If you wish, we can also perform a 100% accurate gender identification during the CVS procedure. There is no additional charge for this service.
How is the sample analysed?
The sample is sent to a highly specialised forensic genetics laboratory for analysis. The sample is analysed using a process known as BOBS (Bacterial artificial chromosomes On Beads) which is a new rapid genetic test for prenatal samples that detects the most common abnormalities.
Sometimes this test is not detailed enough, in which case the consultant will suggest the alternative PCR (Polymerase Chain Reaction) to gain a preliminary result in 3 days followed by karyotyping in a culture. This result takes up to 2 weeks to report and usually produces an identical result to the initial PCR.
Please note the laboratory charges for PCR and culture are greater than for BOBS.
Getting the results
Preliminary results for Down’s Syndrome, Edward’s Syndrome and Patau Syndrome are available in 3-6 days. Culture results, if required will follow in two weeks. Results from a full analysis of other requested chromosomal anomalies can also take up to two weeks.
Most genetic testing produces a definite answer; however in 1 in 100 of cases the results may prove inconclusive so further consultation or testing may be required.
Are there any risks?
There is a 1% risk of miscarriage associated with having a CVS. This means that for every 100 chorion villus sampling procedures it is possible that one patient would miscarry and 99 would be expected to progress normally. Our consultants successfully perform hundreds of CVS procedure every year and their audited miscarriage rates are lower than the national average of 1%.
Because a CVS is performed during early pregnancy when most miscarriages are more likely to occur naturally the risk may be higher than if an amniocentesis is performed in later pregnancy. For this reason we don’t perform the CVS before 12 weeks as the chances of having a miscarriage are much higher.
If you’ve missed the 12-14 week window for the CVS test you can still have an amniocentesis from 16 weeks which also carries a slightly lower risk.