When is the Alpha-Fetoprotein test performed?
During the period of 15 to 20 weeks gestation, about
halfway through pregnancy, many pregnant women are offered
and encouraged to undergo more invasive prenatal testing.
One of the tests available is called the AFP or Alpha-Fetoprotein
test. The AFP test is a blood test used to screen the
baby for certain conditions. The blood taken is that
from mom, but a sample can be obtained for testing from
amniotic fluid. The AFP test is not a diagnosis. It
can only be used to test for the increased likelihood
of an abnormality or birth defect.
What is Alpha-Fetoprotein and why is
the AFP test done?
Alpha-Fetoprotein is a substance produced by the fetus
in utero. AFP stops being produced once the baby is
born. The AFP is excreted in the fetal urine which crosses
into the mother’s blood stream. This is why AFP
can be detected by a blood sample taken from the pregnant
mother.
High levels of AFP can indicate an increased chance
of the fetus having a neural tube defect such as spina
bifida. Another possibility with a high
level of AFP can be a low
level of amniotic fluid surrounding the
fetus. An abnormally low AFP level can indicate an increased
risk of Down syndrome.
The AFP is rarely performed alone. AFP is usually part
of a test called a “triple screen.” The
purpose of the triple screen test is to use the results
of all three blood tests to increase the accuracy of
the results.
There are practically no risks involved with having
the test performed. A simple blood sample is obtained,
generally from a vein in the arm. Bruising is normal
and women who are taking blood thinners or have a clotting
disorder may take longer to stop bleeding from the site.
The accuracy rate of the AFP test is estimated at 80%.
Many times women who under go testing are given results
that indicate a high risk for birth defects and the
baby is born without an abnormality. This is referred
to as a “false positive.”
What happens if you have an abnormal
AFP test?
When a woman’s results return abnormal, an ultrasound
is usually performed. The fetus will then be observed
to find an explanation for the abnormal findings. If
no answers can be found during an ultrasound exam, a
doctor would probably next recommend an amniocentesis.
Many women opt to have the AFP and or triple screen
performed so that if there might be a chance of a problem,
they can be prepared. If a neural tube defect or other
condition is diagnosed, it allows the mother the opportunity
to discuss her options.
Many women also opt out of having blood testing performed
during pregnancy especially the AFP due to the increased
likelihood of a false positive and unnecessary anxiety.
Unless testing is a state requirement, all prenatal
tests are a personal choice that you can consent to
or refuse.
© Rebecca Pillar 2008
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