Chorionic villus sampling
Key points
- Chorionic villus sampling (CVS) is a procedure for taking a small piece of placental tissue (chorionic villi) from the uterus in the early stages of pregnancy to check for the presence of genetic defects in the fetus.
- Depending on where the placenta is located, CVS can be performed through the cervix (transcervical) or through the abdomen (transabdominal).
- Your health care provider will explain the procedure, its risks, and alternative procedures such as amniocentesis.
- A clear, water-based conducting gel is applied to the skin to help with the transmission of the sound waves.
Definition
Chorionic villus sampling (CVS) is a procedure for taking a small piece of placental tissue (chorionic villi) from the uterus in the early stages of pregnancy to check for the presence of genetic defects in the fetus.
How the test is performed
Depending on where the placenta is located, CVS can be performed through the cervix (transcervical) or through the abdomen (transabdominal). The techniques are thought to be equally safe and effective for obtaining samples. Both the transcervical and the transabdominal CVS are performed with ultrasound guidance.
An abdominal ultrasound is performed to determine the position of the uterus, the size of the gestational sac, and the position of the placenta within the uterus. Your vulva, vagina, and cervix are then cleansed with an antiseptic such as Betadine. For the transabdominal procedure, the abdomen is also cleansed.
The transcervical procedure is performed by inserting a thin plastic tube through the vagina and cervix to reach the placenta. Ultrasound is used to help guide the tube into the appropriate area and a small sample of chorionic villus tissue is withdrawn.
The transabdominal procedure is performed by inserting a needle through the abdomen and uterus and into the placenta. Ultrasound is used to help guide the needle, and a small amount of tissue is drawn into the syringe.
The sample is placed in a dish and evaluated in a laboratory.
How to prepare for the test
Your health care provider will explain the procedure, its risks, and alternative procedures such as amniocentesis. Genetic counseling is recommended prior to the procedure. This will allow you to make an unhurried, informed decision regarding options for prenatal diagnosis.
You will be asked to sign a consent form before this procedure, and you may be asked to wear a hospital gown.
The morning of the procedure you may be asked to drink fluids and refrain from urinating to fill your bladder, which allows adequate visualization so the sample may be taken.
How the test will feel
The ultrasound is not uncomfortable. A clear, water-based conducting gel is applied to the skin to help with the transmission of the sound waves. A handheld probe called a transducer is then moved over the area. In addition, your health care provider may apply pressure on your abdomen in an attempt to manually locate the position of your uterus.
The antiseptic cleansing solution will feel cold initially and may irritate your skin if it is not removed after the procedure. Some people are allergic to Betadine. Notify your health care provider if you are allergic to Betadine or if you have any other allergies.
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.