Chorionic Villus Sampling - Information
The information is based on the Royal College of Obstetricians and Gynaecologists (RCOG) guideline Amniocentesis and Chorionic Villus Sampling (published in January 2005). The link is in the section at the bottom of the page.
What is CVS?
CVS is a diagnostic test. It works by allowing the doctors the means of collecting a small amount of tissue from the baby’s placenta (also known as the afterbirth).
Why is CVS carried out?
Placental tissue can analysed (tested) in several different ways and will depend on the reason why CVS is being considered. If parents are worried about a genetic condition, such as Down syndrome, CVS can confirm there is a problem, or reassure that there isn’t.
When is CVS carried out?
This procedure will usually be carried out after 10 weeks and before 14 weeks of pregnancy. In special circumstances it can be carried out later.
How is CVS carried out?
Consent
It is very important that you fully understand all the implications of having a CVS procedure. When you have weighed up all the benefits against the problems associated with having this test for yourself and are absolutely sure you wish to have a CVS test you can proceed.
Pre-procedure preparation
A scan is performed just before the procedure to check:
- the baby measures more than 10 week size (If less than 10 weeks, CVS test will be postponed)
- the position of the baby and placenta (afterbirth)
The area of skin of your abdomen (tummy) covering the site being used for the CVS needle insertion will be thoroughly cleaned. Sterile drapes will then be used to cover most of your abdomen. The scanner head is covered with a sterile plastic bag. The doctors wash and cover their hands with sterile gloves.
All this careful preparation is to ensure that the procedure is carried out in as clean an environment as possible, as this will help to reduce the risk of procedure-related infection to you and your baby.
Procedure
An injection of local anaesthetic is used to numb the skin. A fine needle is passed through the abdominal skin, through the wall of the uterus and into the placenta (afterbirth). This skilled procedure will be carried out under direct scan guidance for the entirety of the procedure.
Once the needle is in the placenta, a small tissue sample is taken by sucking it through the needle. The size of sample taken is very, very small. Taking this amount of placental tissue will not affect the baby, as the placenta is very large compared to the size of the baby at this stage of pregnancy. You will be asked to check your personal details on the label of your CVS sample before it is sent to the laboratory.
Once the procedure is finished, you will be shown the baby’s heartbeat for reassurance.
Post-procedure
A CVS procedure will take 15-20 minutes to be carried out and you will be asked to rest for 15-30 minutes before going home. Some women may feel some discomfort during and following the procedure. It would unwise to leave the hospital if you are feeling uncomfortable or unwell and we would always advise that you rest until you are fit to travel.
Before you leave, details of the timing and how you wish to receive your result will be checked with you, as well as your contact telephone number and address.
We would advise you to rest for two days following a CVS procedure. If you have any worries or concerns please don’t hesitate to contact us at BUPA or the staff at your local Maternity Unit.
If your blood group is Rhesus negative, you will be offered an Anti D injection.
What are some of the common questions parents ask?
Will it hurt?
There will certainly be some discomfort during and for a short time after the CVS procedure. It is not that unusual to have mild period-like cramps after the procedure, but with rest this discomfort will soon wear off.
Will CVS give a definite result?
The CVS will give you a definite result. Exceptions to this, such as culture failure, will be discussed with you during the pre-procedure counselling. Sometimes the result can be unexpected, e.g. a mother may have a CVS based on her concern about having a baby with Down syndrome. The result may be abnormal but not for Down syndrome. Occasionally the result can be difficult to interpret. In these cases, further follow-up is needed, usually by referral to the Medical Genetics Department.
How long does it take to get a result from CVS?
In general it takes up to two weeks for a cultured CVS result but it can be a day or so quicker or slower. If there is a big enough CVS sample, it is possible to give a partial result within 3-4 days. This direct preparation result will only look for major chromosome defects, such as Down or Edwards syndrome. It will not give a complete result. On some rare occasions, the cells collected from the placental tissue sample are very slow to culture. You will be kept informed if this is likely to happen. In these cases it is best just to wait for the slow growing cells to mature or if there is no growth you may want to consider having a repeat test.
Is the procedure dangerous to the baby?
This procedure is ALWAYS carried out under scan guidance. By doing this great care is taken to avoid the areas of the baby that can be seriously damaged by needle-stick injury. In the early days of CVS there were some reported cases of limb defects, but in all these cases the procedure had been carried out before 10 weeks. This is why we insist that the baby is no less than 10 weeks (by scan) when the procedure is carried out.
Following CVS, will the function of the placenta be affected by removing the placental tissue sample?
The amount of tissue removed is very, very small, which is why the sample quality has to be checked before it is sent to the laboratory for analysis.
To support the growing pregnancy, nature has designed the placenta to more than adequately do this and still have lots in reserve. Thus removing a very small sample after 10 weeks will not affect the function of the placenta.
If I were to miscarry, when is this likely to occur?
There is a 1 in 50-100 risk of triggering a miscarriage by carrying out a CVS procedure. Only doctors who are specially trained are allowed to carry out this very skilled procedure. The risk of miscarriage can still be present for several weeks following a CVS. In our experience, it is not uncommon for women to have period-like pain, blood-spotting or fluid loss from the vagina in the first week or so following a CVS procedure. By no means will all these women go on to miscarry, as most symptoms will settle down and the pregnancy will proceed normally.
If you are worried by any symptoms, it is important that you follow the contact instructions contained in – “What you need to look out for following a CVS Procedure” which can be found in the end paragraph.
Is there anything I can do to help prevent miscarriage?
No, not really, but we do advise the following:
- Rest after the procedure and only leave the hospital when you are feeling absolutely fine. Plan to rest for a couple of days but bed rest is not necessary.
- Avoid strenuous tasks or exercise but light duties and gentle walks are fine.
- Avoid intercourse for a couple of days.
- Take pain-killing tablets, such as Paracetamol, if you experience any pain or discomfort. (follow the dosage instructions on Paracetamol packaging).
How should you prepare for a CVS procedure?
It is very important that you fully understand what will be involved in having a CVS test, so be absolutely sure you know what the procedure involves and what the risks are.
Written information and information counselling services are available for you.
Discuss how you would like to have your result given to you i.e. by telephone, by letter or by appointment. It is always wise to discuss with your partner issues surrounding an abnormal result and what your wishes would be in this difficult situation.
Planning for a CVS procedure
- Wear something light, comfortable and that will give easy access to your abdomen, for the procedure.
- You do not need to have a full bladder when attending for an amniocentesis procedure.
- A breakfast or light lunch before the procedure is advised.
- Arrange for someone to come to come with you for your appointment, so they can give you some moral support and to do the driving. We would strongly advise you not to drive yourself home after a CVS procedure. Delays can occur, so be prepared to make contingency plans for the picking up of children etc.
- Arrange to take a couple of days to rest following the procedure, though bed rest is not really necessary.
What you need to look out for following a CVS procedure
You should contact us if you experience any of the following:
- Severe pain that is not controlled with simple analgesia such as Paracetamol tablets.
- Any bleeding, fluid loss or unpleasant discharge from the vagina.
- Abdominal cramps or tightenings
- If you feel that you have a temperature or a very fast pulse.
- If you feel ill or unwell.