What is it?
This is a test in which a few cells are taken
from the developing placenta (chorion) and tested
for chromosomal abnormalities in the baby. It
can be performed as early as 10 weeks onwards.
The main advantage of the CVS test is that results
are normally ready during the early weeks of pregnancy. |
Why Is The Test Done?
This test is advisable for those who are over
35 years of age, in view of the increased risk of the
baby having a chromosomal abnormality such as Down’s
Syndrome. Women with a family history and abnormal blood
tests results are also at higher risk. It is particularly
done for the diagnosis of Thalassemia.
What Will The Test Show?
The cells are tested for chromosomal disorders,
of which Down’s Syndrome is the most important.
If there is a family history of certain inherited
diseases it may be possible to test for these also
especially Thalassemia. CVS will not necessarily exclude
subtle chromosomal abnormalities or mosaicism.
Age
and Risk of Down's |
25 |
1 in 1,500 |
|
38 |
1 in 170 |
30 |
1 in 800 |
|
39 |
1 in 140 |
35 |
1 in 350 |
|
40 |
1 in 100 |
36 |
1 in 300 |
|
45 |
1 in 25 |
37 |
1 in 200 |
|
|
|
How Is It Done?
The test takes place in the Ultrasound room.
You will have the opportunity to ask questions or
discuss any problem with the staff. One relative
may stay with you during the procedure if you wish.
You will have a ultrasound scan before to locate
the position of the placenta. A local anesthetic
will be injected into the skin. Under ultrasound guidance
a fine needle will be passed through the skin and
into the placenta. A tiny piece of tissue is gently
sucked up through the needle. Occasionally it is necessary
to repeat the procedure once more in order to obtain
more tissue. During this time the ultrasound is done
to avoid injuries to the fetus and placenta. The whole
procedure will take about 20 minutes.
Results take one to two weeks. Risks include infection,
bleeding, harm to the fetus, and miscarriage. Long-term
risks of this procedure are unknown.
|
