Women and Newborn Health Service
Health A – Z
King Edward Memorial Hospital
Chorionic Villus Sampling - Fetal Monitoring
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.
Why Should You Consider CVS Testing?
What is the Procedure for Transabdominal CVS?
What is the Procedure for Transcervical CVS?
Will There be Any Pain or Discomfort?
Why Should You Consider CVS Testing?
- You, your partner or another family member has a hereditary condition that may be passed on to your children.
- You are 37 years or older.
- A prenatal screening test (ultrasound or First Trimester Screening) has indicated an increased risk for a birth defect, chromosome anomaly or hereditary condition.
- CVS is also suggested in some situations where partners are closely related or have had two or more miscarriages.
How is CVS Performed?
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.
What is the Procedure for Transabdominal CVS??
- A local anaesthetic is applied to the abdomen.
- A fine hollow needle is passed through the abdomen and uterus into the placenta (chorion).
- The sample of chorionic villi is taken up the hollow needle.
- After the procedure there may be some cramping or bruising of the lower abdomen, however vaginal bleeding is rare. Consult your doctor if bleeding occurs.
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.
What is the Procedure for Transcervical CVS?
This approach does not require a local anaesthetic.
- A speculum is inserted into the vagina to allow a clear view of the cervix. The area is swabbed with antiseptic.
- A fine cannula is inserted through the cervix and uterus into the placenta (chorion).
- A sample of chorionic tissue is taken up through the cannula.
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.
Will There be any Pain or Discomfort?
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.
What are the Risks?
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.
What do the Results Mean?
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.
