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Chorionic
Villus Sampling (CVS) and amniocentesis are ways to collect a sample of the
baby’s cells or fluid to diagnose chromosome problems, birth defects in the
spine or abdomen, and sometimes other genetic conditions.
Chorionic Villus Sampling
This test is
usually done between 10-12 weeks of pregnancy. It involves taking a small
sample of the developing placenta, the tissue  that connects the baby to the wall
of the uterus, using ultrasound to guide the testing. The sample can be
obtained via a needle through the mother's abdomen (A) or using a thin
flexible catheter placed through the cervix (B). The cells in the
placenta usually have the same genetic makeup as the baby does, so they can be
tested to see if the baby has chromosome problems. CVS diagnoses
chromosome problems but does not give any information about birth defects such
as spina bifida. Results take about two weeks.
CVS causes
miscarriages in about 1-1˝ % (2 to 3 in every 200 women) of women who have the
test. CVS is usually not offered before 10 weeks because studies showed
that, if CVS is done before this time, there might be a higher chance (1 in
1000) of causing defects in the baby’s arms or legs. There is also a
slightly higher chance that the results from CVS will be confusing, and other
tests would be needed to understand the results. The main benefit of CVS
is that information about chromosome and other genetic problems is available
early in the pregnancy.
Making
a Decision:
You
are the only one who can decide if any of these tests are the right thing for
you. Some families choose to do only the screening tests; some families
choose to go directly to a test that can diagnose birth defects. Other
families do a combination of tests. The genetic counselors at Eastside
Maternal-Fetal Medicine and your doctor can help you think through this
decision. If you live in the Seattle/King County area, and you would like
to talk more about these tests and making a decision please call us at (425)
688-8111 or (425) 899-2200 to schedule an appointment.
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