|
 |
|
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.
When do I come to the hospital?
CVS is requested much less often than amniocentesis. At BC Women’s, CVS is provided only on Wednesday mornings.
When your doctor or midwife requests this test, we will put your name on a waiting list. We will contact you about a week before the test. If there is no available CVS appointment, you will be offered an appointment for amniocentesis.
You should have a light meal before coming to the hospital. No other special preparation is necessary.
Who will do my procedure?
A doctor who has completed special training in this procedure will do your CVS. A nurse and a sonographer (ultrasound technician) will be assisting.
Who should come with me?
We advise you to not drive yourself or take public transportation (bus) after the test. For this reason, we recommend that your partner, or another person of your choosing, accompany you for your test. You may choose to have that person in the procedure room with you, or, he or she may wait in the lobby, or sit just outside the procedure room. If you have no one to come with you, we recommend that you take a taxi home.
NB. Another adult must accompany children. They may view the baby on ultrasound prior to the procedure, and then wait outside during the test.
What will happen?
Before having your test, a nurse will review the procedure with you and make sure that you are aware of the available options. We will answer any of your questions. She will then obtain your written consent. You will receive information to take home about what to expect after your test.
Ultrasound is used to locate the baby and placenta and to guide during the procedure. The fetus’ heart rate is recorded before (and after) the procedure and some measurements are taken to confirm the number of weeks of pregnancy.
The location of the placenta will determine whether it is possible to do the CVS and the best route for obtaining the sample.
Prior to the test, the area will be cleaned with an antibacterial solution.
- Vaginal route: the doctor will insert a speculum (like when you have a PAP test done), and using a small instrument, take a small sample from the placenta.
- Abdominal: the doctor will insert a fine needle through the abdomen into the placenta, and take a small sample. You may experience some cramping and a slight sensation of pressure.
If it is not possible to do the CVS, we will schedule you for an amniocentesis at the earliest possible appointment, after you have reached 15 weeks of pregnancy.
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 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.
What happens after my procedure?
You do not need to stay in the hospital following your test.
We recommend that you rest for the next 24 hours. You do not have to go to bed. Resting on the couch or in a reclining chair is fine. Avoid heavy lifting and use the time to relax with a favourite book, video, etc. If you need a note to be off work, the doctor who does your procedure will sign this for you.
If you have come from outside the Vancouver area, you may want to consider staying somewhere overnight. If this is not an option for you, “take it easy” (e.g., use the elevator on the ferry or the cart to get to your departure gate at the airport, stretch and take bathroom breaks if you are driving a longer distance).
You will receive written information about what to watch for and how to contact us if you have any concerns. Mild cramping is the most common side effect, and should go away over the next 24 hours.
|
|
|
|
|
|