Chorionic Villus Sampling (CVS)

Before making a choice about prenatal testing, it is helpful to understand the purpose, benefits, limitations, risks and consequences of testing. This information outlines the important information you need to help you decide if you want to have CVS testing.

• Most babies are born healthy regardless of a woman’s age, family history, ethnic background or if prenatal testing was done during her pregnancy.
• Every couple has a 2–3 percent chance of having a baby with some type of birth defect (such as a heart defect, clubfoot, cleft palate). Some birth defects can be corrected after birth and will have little effect on the child’s overall health and development. Other birth defects can be more serious to the child’s overall health. Not all birth defects can be detected in pregnancy.
• Having any prenatal testing in your pregnancy is your choice. Make sure to ask your genetic counsellor or prenatal care provider your questions before making your decision.

What is chorionic villus sampling?

CVS is a diagnostic prenatal test. It is used to detect certain problems with the baby, most commonly it is used to detect chromosome conditions such as Down syndrome.

Who is offered CVS?

• Your first trimester screening (First Trimester Combined Screen or Nuchal Translucency Screen) shows an increased risk for a chromosome condition.*  
• You or your  family  have a history of a pregnancy or child with a chromosome problem.
• Your family has a history of an inherited disorder that CVS can detect

*CVS is only available in Calgary at limited capacity for this indication.

When is CVS done?

The procedure is performed between 11 and 13 weeks 6 days of pregnancy.

How is CVS done?

With the aid of ultrasound, CVS is performed either through the cervix (transcervical CVS) or through the abdomen (transabdominal CVS).

For the transcervical procedure, a thin instrument is inserted into the vagina and through the cervix to reach the chorionic villi (the early placenta). Ultrasound is used to help guide the instrument. A small sample of chorionic villi is removed from the developing placenta. The cells and genetic make-up of the placenta are usually the same as the baby. The cells from this tissue are grown in the laboratory for testing.

The transabdominal approach is similar to amniocentesis. A needle is inserted through the abdomen and uterus and a small amount of chorionic villi is removed. Ultrasound is used to help guide the test.

Is CVS safe?

Most procedures are done without any complications. However, there are risks with the test. CVS may increase the risk of a miscarriage. About 2 percent of pregnancies are naturally lost to miscarriage after the 10th week of pregnancy. Having a CVS increases this risk by another 1 percent.

Other problems that can occur from CVS are bleeding, cramping, leaking of amniotic fluid, and infection. The risk of these is low (about 1 percent or less).

Only rarely is the test is not able to give an accurate result. In these cases, amniocentesis is usually recommended.

How do I prepare for CVS?

You do not have to do anything to prepare on the day of your test. When you arrive for your appointment, please do not empty your bladder until one of our staff asks you to.

Prior to your CVS, you will meet with a nurse who will review the procedure with you and address any questions you may have.

What happens after the procedure?

Avoid strenuous activity (e.g. vacuuming) for 1 to 2 days after the procedure. You may have a small amount of bloody spotting for up to a week, especially if you had the transcervical procedure.

• a fever
• painful contractions or worsening abdominal pain.
• unusual or bloody drainage from the vagina (If you have vaginal discharge, wear a sanitary pad and bring it in to show your doctor.)

What are the benefits of CVS?

With CVS, you will usually receive your results before your 15th week of pregnancy. For the most part, the results are reassuring, giving you peace of mind for the rest of the pregnancy.

How long will it take to get my results?

Results take 2-3 weeks and will be given to you by your family doctor or the obstetrician who did your test.

What can affect the results of the test?

Problems, though uncommon, may come up during the procedure or in the laboratory. Your obstetrician will discuss the problem and the options available to you. Problems may include:

• a technical difficulty getting the chorionic villus sample
• the cells do not grow, so no result is possible
• trouble interpreting the test results (you and your partner may be asked to give a blood sample to help interpret your baby’s chromosome result)

What are the differences between CVS and amniocentesis?

• CVS can be done earlier (at 10-13 weeks). Amniocentesis is done after 15 weeks.
• You usually have the results before your 15th week of pregnancy.
• CVS removes tissue from the developing placenta. Amniocentesis removes amniotic fluid surrounding the baby.
• Amniocentesis screens for neural tube defects: CVS does not. However, the recommended 18-20 week ultrasound will pick up most serious birth defects, including neural tube defects.
• The risk for miscarriage may be slightly higher with CVS (1%) than with amniocentesis (0.5%).

Do normal results mean that my baby will be born healthy?

Most women receive a normal result, which takes a lot of the worry out of the pregnancy as CVS provides accurate information about chromosome conditions. However, no prenatal test can guarantee the birth of a healthy baby. Of 100 babies born, 2 to 3 would have a birth defect that is not caused by a chromosome condition and not be diagnosed by amniocentesis or CVS.

What happens if a problem with my baby is found?

Your prenatal care provider and/or the Prenatal Genetics Clinic offer genetic counselling and support. The purpose of the counselling is to review the results and provide all the support and information necessary to help women/couples make decisions about their pregnancy management.

Where can I can more information?

In Calgary, contact the Prenatal Genetics Clinic in Calgary at (403) 943-8375.