CVS Testing (Chorionic Villus Sampling)

What is a CVS test?

Chorionic villus sampling is a test that samples or biopsies the developing placenta. This is usually done to carry out testing for chromosome abnormalities like Down Syndrome or doing genetic testing in a family with a known genetic disease.

It is done between 11 and 14 weeks by passing a very fine needle through the wall of the womb under ultrasound guidance or introducing a fine catheter through the cervix, depending on the position of the placenta, and taking a small sample of the placental tissue.

It provides a way of doing very accurate testing for chromosomal and genetic problems.

It is associated with a small risk of miscarriage estimated at a 1% chance.

How is the test performed?

If done through the abdomen local anaesthetic is injected first. The sampling needle is then passed into the placenta using the visual guidance of an ultrasound done at the same time. A drawing or tight feeling in the pelvis or side is common when the needle enters the placenta and the biopsy is taken.

A CVS done vaginally feels similar to a PAP smear. The main discomfort involved in a transvcervical CVS is the sensation of the speculum which stretches the vagina to allow the cervix to be seen.

After the test is finished the sonographer will check that the baby is OK. This is mainly for the parent’s reassurance as a CVS is always done well away from the baby.

What testing is done on the sample?

The most common indication for an CVS is testing for chromosomal problems like Down syndrome. The risk of Down syndrome may be considered high when nuchal screening results from the 12 week scan have suggested a high risk, if the mother is >35 years or when there is a known chromosomal abnormality in the parents.

Two tests are run on the sample – one a rapid simple check and the other a longer culture test.

The rapid test looks for simple, common problems that involve an extra or missing major chromosome. This is in fact what causes most forms of Down syndrome. We will phone these results through to you within 2 working days of the amniocentesis. If we are doing the test because of a high risk nuchal result in a baby that looks normally formed then the results of a normal rapid test are extremely reliable.

The culture test allows the scientist to check all the chromosomes more thoroughly and takes about 2 weeks to report. It allows us to double check the Down’s result and also to look for rarer problems that relate to breakages or rearrangements of chromosomes.

More complex genetic testing on amniotic fluid for familial conditions may need to be sent to laboratories interstate and can take longer. Often we will do this in consultation with genetic specialists from Nepean Hospital and will keep you informed of results as they arrive.

ON THE DAY

We suggest you come with a family member or friend who can take you home. Although most women are capable of driving themselves home, the moral support and help of a companion and driver is very valuable. You will have the chance to speak with our doctor before the test to go over the reasons for the test and what is involved. You will then be taken into one of the scanning rooms where they baby will be checked and a decision made as to the best way of approaching the placenta – transabdominally or transvaginally. If done transvaginally you will be allowed to empty your bladder. After the test most women are fine to go straight home but there is the opportunity to sit quietly for a time if needed. In the next few hours you may experience some period like cramps. Simple pain tablets like paracetamol and rest usually work well. It is best to arrange the day off work in case you feel uncomfortable. The risk period for miscarriage is roughly 2 weeks with the riskiest time in the 3 days after the test. Symptoms to watch for are persistent fever, persistent or worsening cramps and vaginal bleeding or foul smelling discharge. If any of these happens please notify us and your doctor so we can assess the situation.

We suggest you come with a family member or friend who can take you home. Although most women are capable of driving themselves home, the moral support and help of a companion and driver is very valuable.

You will have the chance to speak with our doctor before the test to go over the reasons for the test and what is involved. You will then be taken into one of the scanning rooms where they baby will be checked and a decision made as to the best way of approaching the placenta – transabdominally or transvaginally.

If done transvaginally you will be allowed to empty your bladder.

After the test most women are fine to go straight home but there is the opportunity to sit quietly for a time if needed.

In the next few hours you may experience some period like cramps. Simple pain tablets like paracetamol and rest usually work well. It is best to arrange the day off work in case you feel uncomfortable.

The risk period for miscarriage is roughly 2 weeks with the riskiest time in the 3 days after the test. Symptoms to watch for are persistent fever, persistent or worsening cramps and vaginal bleeding or foul smelling discharge. If any of these happens please notify us and your doctor so we can assess the situation.

If you have any concerns, our doctors can be contacted at the practice you attended.

IMPORTANT POINTS

Arrange help or time off work on the day of the test

We need to know your blood group. This is often on your yellow cardor in your doctor’s records – please bring with you.

Women with a Rhesus negative blood group need an injection of antiD after the procedure.

Let our staff know if you take aspirin or Clexane as we may need these stopped a few days before the test.

The laboratory will send you a separate bill, a significant amount of which will be refundable by Medicare. The results will be phoned through to you by our doctor

If you have any concerns please contact the practice you attended to speak with one of our doctors.