Chorionic villus sampling (CVS)
You will be offered CVS if your baby is at high risk of having a genetic disorder. This might have been detected by an early screening test or might be because you have a family history of certain conditions or have had a previous pregnancy affected by a genetic disorder. The decision - like all pregnancy screening - is up to you.
• Pregnancy home page
• Week by week pregnancy calendar
• Antenatal appointments
• Nuchal scan
• 20-week scan
The test can be taken earlier than amniocentesis, so may identify any disorders at an earlier stage in your pregnancy.
What happens during CVS?
A sample of chorionic villi cells is taken from the placenta using a needle, which is either inserted through the abdomen or through the cervix. The chorionic villi 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 five minutes and may cause discomfort but is not particularly painful. You will be told to take it easy for a couple of days and you may experience some cramping after the procedure. The initial test results can come back in a few days but the full results can take up to a month.
What does CVS show?
- Genetic abnormalities such as Down's syndrome
- Cystic fibrosis
- Muscular dystrophy
- Inherited blood disorders such as sickle cell anaemia and thlassaemia
- Metabolic disorders such as antitrypsin deficiency
- Mental health conditions such as fragile X syndrome
CVS doesn't test for physical problems such as spina bifida.
What are the risks of CVS? Is it safe?
CVS is an invasive procedure and so carries risks. 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%.
Things to ask before CVS or amnio:
- Who will be doing the test?
- How many have they done before?
- What is their miscarriage rate?
There is also a risk of infection, although according to the NHS Choices severe cases only occur in less than 1:1,000 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.
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 and throw all your future projections about your baby and your familiy into disarray. You should be offered counseling 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. Mumsnet can help - umpteen women on the Talk boards have gone through similar circumstances and have advice and insights.
What Mumsnetters say about CVS
- I had a CVS with my daughter after a 1:12 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. Chynah
- 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 your decision. geekgrrl
- 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. It was the longest two weeks of my life. Our CVS results came back clear. Our daughter is perfectly healthy. Porridgebrain