Chorion villus sampling
What is chorion villus sampling?
Chorion villus sampling (CVS) is an invasive diagnostic procedure that involves the examination of the chorionic villi (placental tissue) to look at the chromosomes of the baby. Both the baby and placenta originate from the same cell and so the chromosomes present in the cells of the placenta are the same as those of the baby.
Why is CVS offered?
- Positive screening test including nuchal translucency risk assessment and/or NIPT
- Maternal age: some women older than 35 year declined screening tests in lieu of a definitive test
- Previous history of an affected child, parental chromosomal abnormalities or rare genetic diseases
How is CVS performed?
You will have the procedure explained to you by our specialist doctor and sign a consent form. Local anaesthetic is injected into the abdomen and a fine needle is then passed through the abdomen into the placenta and a sample is aspirated. The needle is carefully observed using ultrasound to ensure the sample is taken from the correct place. The procedure takes approximately 5 minutes and afterwards we check that the fetal heart beat is normal.
What should I expect after the CVS?
For the first couple of days you may experience some abdominal discomfort, crampy period-like pain or slight bleeding. These are relatively common and in the vast majority of cases the pregnancy continues without any problems.
You may find it helpful to take simple analgesia such as paracetamol.
If there is a lot of pain or bleeding or if you develop a temperature please seek medical advice.
When can I expect to get the results?
Chromosomes contain our DNA that give instructions to our cells on how to form, develop and functions. Changes in our chromosomes and DNA can therefore lead to developmental defects and also affect function. There are a number of tests that will be considered:
- Fast FISH: Special dying technique to give answer within 24-48 hours on the most common chromosome abnormalities involving chromosomes 21, 18, 13 X & Y. It provides a rapid answer on the risk of Down syndrome
- Karyotype: Cells are cultured in a medium then fixed and stained. This test will count all chromosomes and report on some structures changes called deletion(missing DNA) and duplications(extra DNA) as well as translocations (exchange of DNA). This result takes 2-3 weeks to become available.
- Chromosome micro-array testing(CMA): This is the latest laboratory technology that allow us detailed information about missing or extra DNA. This result takes 2-3 weeks to become available.
A patient will receive a personal phone call to discuss results and options and we will facilitate additional opinions if required.
What are the risks associated with the test?
The risk of miscarriage due to CVS is about 0.5% and this is the same as the risk from amniocentesis at 16 weeks. If you were to miscarry due to the CVS, this would happen within the next five days.In approximately 1% of cases the invasive test will need to be repeated because the results are inconclusive.