Alpha Feto-protein (AFP)
What is the AFP test
This is a blood test that measures the
amount of alpha-foeto protein (AFP) in the mother’s blood and the amniotic fluid. It
is generally performed in the 15th to 18th week of pregnancy. High levels of AFP could
indicate that the baby has a neural tube defect (NTD). This defect manifests itself as
spina bifida (deformity of the spinal column) or anencephaly (the absence of all or part
of the brain). Abnormally low levels could be a sign of increased risk of Down’s
syndrome or other chromosomal defect. 95% of the time there is no past family history of
these conditions.
How accurate is the AFP test
The drawback of this test is that
abnormally high or low levels of AFP in the blood do not necessarily indicate that your
baby will have a birth defect. Statistics show that while only 1 to 2 women in a 1000 have
a foetus with a neural tube defect (NTD), about 50 of these women will demonstrate high
levels of AFP in their blood when tested. Thus, to make a positive diagnosis, further
testing such as amniocentesis and a sonogram becomes necessary. An elevated level of AFP
in the amniotic fluid is associated with a 90 % chance that the foetus has NTD.
Amniocentesis
What is amniocentesis and how is it
performed
This test is helpful in diagnosing birth
defects such as neural tube defect (NTD), including anencephaly (failure of brain
formation) and spina bifida (open spine). A small sample of the fluid in which the
baby lies is drawn off through a needle. The test measures the amount of fetal
protein both in the mother’s blood as well as in the amniotic fluid surrounding the
baby.
For whom is amniocentesis advised
An amniocentesis is usually advised for
women in the following high risk category for birth defects:
- Women over 35 (since the risk of Down’s
syndrome is very high)
- Women with three or more miscarriages
- If either parent or sibling has a known
chromosomal abnormality or a hereditary disease
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