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Chorionic Villus Sampling

Chorionic Villus Sampling

Chorionic villi form as part of the placenta and are made up of cells that develop from the fertilized egg that has developed into the fetus. Chorionic villi contain the same genes as the fetus and can be examined to rule out chromosomal disorders. Unlike amniocentesis, chorionic villus sampling does not provide information about neural tube defects. (this can be done later by drawing and testing a blood sample from the mother).   

Chorionic villus sampling (CVS) involves taking a small sample of tissue for testing in the lab. and is usually done between the tenth and twelfth weeks of pregnancy.  More information can be found below and on the Prenatal Genetic Screening Program website.

What it detects

What can CVS detect?

CVS is a specific test that is able to tell if your baby has a normal number of chromosomes (46). It can find Down syndrome and other major chromosome abnormalities. 

Unlike amniocentesis, it cannot measure the amount of alpha-fetoprotein (AFP) in the amniotic fluid. You will be booked for a blood test at a later date to screen for neural tube defects, such as spina bifida.
Normal results can take up to three weeks. Concerns are usually identified and given to your doctor or midwife within 10 -14 days.
If there is a family history of a known problem, other special tests may be done on the sample. You need to discuss this with your doctor or midwife who will refer you to Medical Genetics so that arrangements for additional tests can be planned in advance of your procedure.

Five in 100 women have a chance of having a baby with a major birth defect that can be found during the first year of life. The most common defects are cleft lip and palate, clubfeet, heart defects and mental retardation. The results from amniocentesis, CVS or fetal blood sampling will indicate whether or not there are chromosome abnormalities or neural tube defects, but will not be able to rule out other abnormalities.

What are the risks

What are the risks involved in CVS?
  • Risk of Miscarriage: The risk of miscarriage unrelated to any procedure is about 6 in 100 at 9 to 12 weeks of pregnancy. Following CVS the average increased risk of miscarriage is between 1 and 2 in 100.
  • Infection: There is always a risk of infection following any type of medical procedure. During CVS, care is taken to make this risk as low as possible. Signs of infection are fever or flu-like symptoms, which require medical attention.
  • Bleeding, Leaking Fluid or cramping following the procedure: Mild cramping is the most common side effect, and should disappear within 24 hours. Some spotting (light bleeding) is common following a vaginal CVS. If you are concerned about bleeding or fluid leaking, you may call your doctor or midwife for advice.
  • Harm To The Fetus: Studies have shown a possible increased risk of malformations in the limbs (arms, legs, hands, or feet) of the fetus following CVS (the risk with no procedure is 1 in every 2000 to 5000 births, following CVS it appears to be 1 per 1000 to 2000 births). However, this appears to be primarily when the test is performed on women before their 10th week of pregnancy, which is not generally done at our centre.
  • Failure to Obtain Results: Sometimes the test must be repeated because the cells do not grow in the laboratory, or there are not enough cells in the sample.
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