Chorionic villus sampling

Chorionic Villus Sampling, or CVS, is one type of diagnostic testing that is available in Ontario during the pregnancy. CVS can be done between 11 to 14 weeks in the pregnancy (first trimester), and can give you definitive answers about the conditions you choose to have testing for.

Who Can Have CVS

Reasons why you may be thinking about having CVS include:

you got a "screen positive" result from enhanced First Trimester Screening (eFTS).
you got a "high risk" result or a failed result, from Non-Invasive Prenatal Testing (NIPT).
your 11-14 week (Nuchal Translucency) ultrasound picked up a difference in the growth or development of the baby. For example, the nuchal translucency is increased compared to what what we typically see.
there is a specific genetic condition running in your family, and you wish to have the baby tested for it before birth.

How to Get CVS

If you are interested in CVS, speak to your health-care provider about referring you to a specialist in genetics. There, you will get more information about this OHIP-funded test, and the team will arrange it if it is an appropriate test for you.

Find a Local Genetics Centre

How It Works

CVS is done at specialized centres in Ontario by trained doctors. An ultrasound is performed to show the physician the location of the baby and of the placenta (the organ that connects you to the baby).

There are two ways that CVS can be done, depending on the position of the placenta and the expertise of the doctor:

"Transcervical" (most common way) - a special tool is passed through the vagina and the cervix to get to the placenta.
"Transabdominal" - a needle is inserted through the abdomen and uterus (womb) to get to the placenta.

Through either way, a small piece of tissue is taken from the placenta and sent to the lab for testing. The tissue from the placenta usually contains the same genetic information as the baby.

Transcervical CVS

The procedure generally takes a few minutes. Some people experience brief discomfort such as a cramping sensation. You will likely be able to return to your regular activities within one to two days after the CVS.

What to Expect After CVS

There is a risk of miscarriage (losing the pregnancy) from CVS which can make it difficult to decide whether to have this procedure. It is important to remember that there is always the chance of pregnancy loss in the first trimester of pregnancy even if CVS is not done. CVS increases this risk by less than 1%. CVS does not cause other complications for the baby (such as birth defects).

Results

The type of results depends on which centre did the CVS and what testing is ordered. It is important to speak with your genetics specialist about what your results will include.

Rapid Results (also called QF-PCR)

Typically, you will receive a a set of results 3-4 days after the CVS. These results can tell you if the baby has one of the following chromosome differences: trisomy 21, trisomy 18 or trisomy 13 or a sex chromosome difference.

Depending on the hospital and the reason for testing, your testing may stop at this point or there may be additional tests done from the same piece of tissue:

Microarray test

This test will tell you whether there are pieces of other chromosomes that are extra or missing. These are chromosome differences that can run in families, but usually happen by chance in the sperm or the egg that made the baby. These chromosome differences do not happen more often as the pregnant individual gets older.

The results from microarray test take approximately 2-3 weeks, but you can check with their health-care provider when to expect results.

Video on Chromosomal Microarray Testing

A short video created by Alberta Health Services, explaining the microarray test and possible results. In this video, the testing was done through a blood draw. The way the test works and type of results are the same when the microarray is done through CVS.

Other genetic conditions

Other genetic conditions can be tested if there are other concerns - e.g. there are certain signs on one of your ultrasounds, or there is a particular genetic condition running in the family (such as cystic fibrosis or sickle cell anemia).

All CVS results are sent directly to the genetics specialist who organized the test.

Benefits

There are several benefits to CVS:

Diagnostic - can give a “yes” or “no” answer about chromosome differences.
Tests for more conditions - can test for more genetic conditions compared to available screening tests, including NIPT.
Quick results - results on trisomy 21, trisomy 18, trisomy 13 are available faster than available screening tests.
Earlier results - gives results earlier than amniocentesis because CVS is done in the first trimester of pregnancy.

Limitations

There are several limitations to CVS:

Cannot test for everything - CVS cannot test for every possible genetic condition and will not give you information about any differences in the physical development of the baby (e.g. cannot pick up heart or kidney defects). Ultrasounds are still recommended to look for physical differences.
Getting results that you do not expect or are difficult to interpret - rarely, we get results from CVS that are difficult to interpret, which means it may be hard to know what the genetic difference that we see means for the baby's health or development.
Tests the DNA (genetic material) from the placenta, not the baby - the placenta and the baby usually have the same genetic information (which means the same number of chromosomes), but this is not always the case. In rare cases, it will be recommended that an amniocentesis is done as a follow-up test to get definitive information. Amniocentesis looks at the DNA directly from the baby.