|Procedure: Chronic Villi Sampling|
Description and Purpose
Chronic or chorionic villus sampling , is
where, in order to obtain cells from the
surface, a thin catheter is inserted into the
and and a sampling
of cells is suctioned into the tube.
is used to guide placement of the catheter. The purpose of this procedure
- To detect suspected in the foetus.
- To identify chromosome disorders, most commonly in women over 35.
Preparation and Procedure
If the test is undertaken in the first trimester, a full bladder is required,
as it helps push the uterus out of the pelvis and thus gives a better
An ultrasound is used to observe the position of the uterus and placenta,
both of which help determine whether a catheter will be inserted through
the vagina and cervix or a needle inserted through the abdomen and uterine
wall. If the sample is taken through the uterine wall, a local anaesthetic
may be applied first.
For the needle method, an is placed on the abdomen as in .
For the catheter method, a thin metal rod is inserted into the cervix
to help identify it on the ultrasound scan and show how best to insert
the catheter into the uterus.
- Can be performed earlier in
(at around ten weeks).
- It is almost 100% reliable
in detecting chromosomal and genetic defects.
- It does not measure
(AFP), so a supplemental blood test must be used.
- It entails a slightly higher risk of
than does amniocentesis (1%-2% greater).
- It's less commonly available than amniocentesis,
and fewer doctors are experienced in the procedure.
- It entails a greater risk of distorted results than
does amniocentesis due to presence of mother's cells
in the sample and discrepancies between chorionic
villi and foetal genes.
- Metabolic disorders are difficult to diagnose and
must be confirmed with amniocentesis.
- Because of the early gestational age at which the
test is performed, foetal anatomy cannot be seen as
well as it can at the time amniocentesis is performed.
The information in this page is presented in summarised form and has been taken
from the following source(s):
The Yale University School of Medicine Patient's Guide to
Medical Tests, Barry L. Zaret M.D., Senior Editor, published by Houghton Mifflin.
(def;articles & more)