Chorionic villus sampling (CVS) involves taking a small amount of placental tissue (chorionic villi) which has the same genetic information as the fetus for analysis in the laboratory. Hereditary conditions passed on by the genes from parent to child (such as Duchenne muscular dystrophy) and chromosome abnormalites (such as Down syndrome) can be tested. The CVS results are 99% accurate in confirming or excluding ONLY the specific condition/s being tested.
Further information and additional resources can be obtained from the Maternal Fetal Medicine Service.
Ultrasound guidance is used to obtain a small tissue sample either through the abdomen (transabdominal) or through the cervix (transcervical) depending on the position of the uterus and the placenta.
The following is a diagram of the transabdominal chorionic villus sample (CVS) procedure.
Please click to view the MPEG video that shows ultrasound images during a Chorionic Villus Sampling (CVS) in the first trimester. It is 4.7MB in size and will take approximately 12 minutes to download using a 56K modem.
This approach does not require a local anaesthetic.
You may experience light vaginal bleeding after the procedure. Contact your doctor if bleeding is persistent or heavy.
The following is a diagram of the transcervical chorinic villus sample (CVS) procedure.
You will be awake during either procedure and should experience only a little or no pain. Discomfort such as pressure or menstrual cramp has been described. There may be tenderness at the insertion site. It is recommended that you rest for a few minutes after the procedure and take things easy for several days but bed rest is not required.
The risk of fetal loss is 1- 2% as a result of chorionic villus sampling under ultrasound guidance. That means there are between 1 and 2 chances of miscarriage for every 100 sampling tests done. If there is any abdominal pain, or loss of blood or fluid from the vagina following the procedure, your doctor should be consulted. There is not considered to be any risk to the fetus from the needle when the procedure is guided by ultrasound.
Results from CVS can take up to two weeks for the cells to be grown in the laboratory and the test to be analysed. A negative result excludes ONLY the condition for which the test was performed. This does not guarantee the absence of other different birth defect/s. There is NO test to exclude all pregnancy abnormalities.