When and how is chorionic villus sampling performed?
Chorionic villus sampling is usually performed between 10 and 13 weeks of pregnancy. This is usually a transcervical/transvaginal CVS, and a transabdominal CVS may be performed from 13 weeks onwards.
You will need a full bladder for chorionic villus sampling and the main steps involved are:
An ultrasound scan will tell you how many weeks pregnant you are and will determine the position of the placenta. Once that’s done, the doctor will be able to decide whether it’s best for you to have a transvaginal or transabdominal CVS.
Ultrasound will be used as a guide throughout and to check the baby afterwards:
During transvaginal CVS, your doctor inserts a pair of fine forceps or a small tube into your vagina and through your cervix to the placenta.
During transabdominal CVS, a needle is pushed through your abdomen and inserted into your uterus to reach the placenta. You may be given a local anaesthetic for this method of chorionic villus sampling to reduce discomfort.
A small sample of cells is then taken from the placenta and removed for testing.
The CVS test takes around 20 minutes to perform in total, and results are usually available within 1 to 2 weeks, but can take up to 3 weeks if the test needs to be sent away.
Dealing with the results of chorionic villus sampling
The test results from a CVS will show if your baby has a known genetic or inherited abnormality. The DNA analysis of the cells taken from the chorionic villus will show if your child will be born to face disability or a lower life expectancy. You will then be given plenty of support to decide what to do. This is a very personal decision and full of anguish for both parents and their families. You will be given counselling and advice but the choice of whether to keep your child, or whether to have a planned termination will, ultimately, depend on how you and your partner feel.
What are the advantages of chorionic villus sampling compared with amniocentesis?
CVS can be performed earlier in pregnancy than amniocentesis, which is generally only performed in the second trimester. It therefore offers an earlier opportunity to make choices if a foetal abnormality is detected.
However, it is important to remember that, unlike amniocentesis, CVS does not test for structural problems such as neural tube defects. Therefore, it is important for you to have blood tests for serum alpha-fetoprotein and other diagnostic tests if screening for neural tube defects is considered necessary.
Are there any risks involved with chorionic villus sampling?
Approximately 0.5–2% of women miscarry as a result of CVS. The CVS procedure can sometimes cause bleeding or infection. In particular, the transvaginal method can sometimes lead to cervical polyps or fibroids, or problems with the position of the placenta. There are risks of limb deformities when CVS is performed earlier than 10 weeks into pregnancy, and so the procedure is generally not carried until 10 weeks or later.
Women with HIV are at increased risk of passing the virus to their baby if a CVS is performed, and so the procedure is best avoided if you are HIV positive.
Is chorionic villus sampling right for me?
Having a diagnostic test can be emotionally and physically demanding. It is important to discuss with your doctor the disorders that CVS can test for, how it will be carried out, the risks, and possible outcomes, as well as the choices you will have afterwards. Your doctor will take all the medical information available into account when advising you whether the CVS test is suitable but the final decision is yours.
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Dr Kathryn Senior is an acclaimed medical journalist who has written over 500 feature articles for leading international journals within The Lancet group. As Senior Writer at Freelance Copy she produces high quality scientific and medical content for websites and printed publications for companies and organisations in the health, medical and pharmaceutical sectors.