Chorionic villus sampling (CVS) is a test offered between week 10 and week 13 that can check whether your baby has a genetic or chromosomal condition such as Down's Syndrome, Edwards' Syndrome and Patau's syndrome. The test involves taking a small sample of cells from the placenta. As with all tests during pregnancy, whether you want to have it is up to you.
Will I be offered CVS?
The CVS test is not offered routinely to pregnant women, so you'll likely be offered it if your baby is at high risk of having a genetic or chromosomal condition. Try not to worry too much if you are offered the test – a risk is not necessarily a guarantee.
There are two types of test that take place during pregnancy: screening and diagnostic. CVS is a diagnostic test, which offers more information than a screening test. Screening tests pick up indications that your baby might be at higher risk of certain conditions. If in one of your screening tests these clues are picked up, then you might be offered diagnostic tests, often a choice between amniocentesis and CVS.
CVS is likely to be offered if you have a family history of certain conditions, such as:
- Sickle cell anaemia
- Cystic fibrosis
- Muscular dystrophy
- A previous pregnancy affected by a genetic disorder
The test might also be suggested to you if you are an older mother, such as if you're pregnant and over 40, because your risk increases with age.
I had a CVS with my daughter after a one-in-12 risk for Downs (I was 40). The test was uncomfortable rather than painful and over very quickly and I saw my baby on the scan afterwards to check she was OK. Got the preliminary results two days later and the full set two weeks after. My results were, thankfully, clear.
The decision to have the test, like all pregnancy screening, is entirely up to you. The test can be taken earlier than amniocentesis, so may identify any disorders at an earlier stage in your pregnancy. Your midwife or doctor will tell you all about what the test involves and what the possible benefits and risks are to help you make an informed decision. Check with your hospital, but you might want to bring along your partner or a friend for some support when you have the test.
What happens during CVS?
A sample of chorionic villi cells is taken from the placenta using a needle. The needle will either be inserted through the abdomen (transabdominal, the most common method) or through the cervix (transcervical). The transcervical method of CVS testing carries a slightly higher risk of vaginal bleeding after it is carried out, so is less commonly used. It occurs in one in 10 women who have this procedure. Your healthcare team might use it if it is easier to access the placenta. The NHS says that there is no difference in the number of miscarriages between the two methods.I had a CVS, it was uncomfortable rather than painful, and alarming to see the needle on the ultrasound, being jiggled about. I had some bruising and a bit of a sore feeling for a week or so. Bear in mind that you won't 'need' a CVS – it's your baby and it's your decision.
If you have CVS via the transabdominal method, you will be given a local anaesthetic. Your stomach will be cleaned and ultrasound will be used to guide the needle. Attached to the needle is a syringe, in which a small amount of tissue will be collected and sent off to the lab for testing.
CVS carried out via the transcervical route involves a thin tube that is attached to a syringe, or small forceps, being inserted through the vagina and cervix. It is then guided towards the placenta using the ultrasound scan.
How ever the scan is carried out, the test samples chorionic villi, which attach the placenta to the wall of the womb. They are made from part of the embryo that separates during early cell division and so they have exactly the same DNA as the foetus.
The test takes about 10 minutes and may cause some discomfort but is not particularly painful. The whole consultation may take around 30 minutes in total. You will be told to take it easy for a couple of days and you may experience some cramping after the procedure.
How will I feel after the test?
You will be monitored for up to an hour after the test, just in case you have any side effects such as heavy bleeding. You can then go home to rest. It's likely you’ll want a lift home as you might not feel up to making the journey alone.
It's normal to have cramps after CVS that feel a bit like period pain. You might also have some light spotting for a couple of days. If it's uncomfortable, you can take paracetamol – but don't take aspirin or ibuprofen. Take it easy for the rest of the day.
You should contact your midwife or the hospital where you had the scan for advice if you develop any of the following symptoms:
- Persistent or severe pain
- A high temperature of 38c or above
- Chills or shivering
- Heavy vaginal bleeding
- Discharge of clear fluid from the vagina
What does CVS show?
CVS can detect a large number of conditions, including, but not limited to, the following:
- Genetic abnormalities such as Down's syndrome
- Cystic fibrosis
- Muscular dystrophy
- Inherited blood disorders such as sickle cell anaemia and thalassaemia
- Metabolic disorders such as antitrypsin deficiency
- Developmental disorders such as fragile X syndrome
- Phenylketonuria – a rare condition where the body cannot break down a substance called phenylalanine, which can build up to dangerous levels in the brain
CVS does not detect neural tube defects such as spina bifida, Rhesus incompatibility, or birth defects such as cleft palate.
What do the results of a CVS test mean?
You should talk through the results of the test with your midwife or doctor so that you can ask any questions you might have about the health of yourself and your baby. The initial test results can come back in a few days but the full results can take up to a month, depending on what you have been tested for.We were given a one-in-13 chance of Down's syndrome, and a risk of a heart defect. We had to wait a week for the CVS test as I was bleeding internally and another week for results
A “normal” result means there are no signs of genetic defects in the developing baby. However, even though the tests are very accurate, no test is 100% accurate at testing for genetic issues in a pregnancy.
CVS testing can be used to detect a multitude of genetic conditions, so an “abnormal result” could be due to any of them. Talk to your midwife or doctor about how the condition may be treated either during or after the pregnancy and what special needs your child may have after birth.
What are the risks of CVS? Is it safe?
CVS is an invasive procedure and so carries some risks to be aware of. You shouldn't worry unduly though, and it will be carried out by experts in the field who do this all day long, so they are usually well-practised and hugely experienced. There is an increased risk of miscarriage, which has been estimated to be 2% more than the risk of miscarrying without a CVS procedure. This makes CVS slightly more risky than an amnio, which has an additional risk of 1%.
There is also a risk of infection, although according to the NHS, severe cases only occur in less than one in 1000 procedures. If you are rhesus negative, CVS carries a risk of sensitisation, which may trigger an immune response against your baby. You will be offered an Anti-D injection to counteract this and this might be followed up with an ultrasound scan two to four days after the procedure to make sure everything is going ok.
CVS will not be carried out before 10 weeks gestation because there is thought to be an added risk of damaging the baby's limbs before this stage of development.
What are your options after getting CVS results?
CVS is said to be 99% accurate, although not every abnormality can be ruled out by the test. If an abnormality is found, it can be very upsetting. You should be offered counselling to help you cope.
If you decide to end your pregnancy, your GP and midwife will be able to go through your options with you. If you decide to carry on, it's worth finding out as much as you can about the disorder and how you can care for your baby before the birth. Take your time in making any decision, you should treat yourself with the utmost kindness and go with what is right for you.