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Elevated alpha-fetoprotein (fetal protein) in the mother's - blood biochemical screening
test
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The level of alpha-fetoprotein in the mother's blood is considered to be elevated
if it is more than 2.5 times the average in a singleton pregnancy, and more than
twice the average in a twin pregnancy. It can arise from a number of causes:
- In the vast majority of cases (98%), it results from a transient placental problem
such as a slight separation of or mild bleeding from the placenta. This leads to
the passage of a relatively increased amount of fetal blood, which contains fetal
protein, into the mother's bloodstream, thus resulting in elevated levels of alpha-fetoprotein
in the mother's blood. This usually disappears when the placental problem is resolved.
In these cases, the alpha-fetoprotein level in the amniotic fluid will, of course,
be normal. Similarly, if the alpha-fetoprotein level in the mother's blood is measured
5 - 11 days after amniocentesis,
it may also be found to be elevated for the same reason, i.e. transfer of fetal
blood into the maternal blood.
- In a small number of cases, the calculation of the alpha-fetoprotein level in the
mother's blood is based on an inaccurate assessment of the gestational age. When
this is corrected the level may well be found to be normal.
- In a small number of cases (2%) there may be a defect in the fetus that causes an
increase in the level of alpha-fetoprotein, initially in the fetus's blood and the
amniotic fluid, and secondarily in the mother's blood. Common conditions where this
can occur include defects in the closure of the spinal canal ( neural tube defects [NTD's]); kidney defects
leading to increased secretion of protein in the urine, such as can happen in a
rare, severe kidney disease that progresses to renal insufficiency in infancy; failure
of closure of the abdominal wall, and
other defects in the intactness of the fetal skin (congenital skin disease, etc).
- In cases of multiple gestation, where one fetus stops developing (usually after
the 10th week), an elevated level of alpha-fetoprotein can be expected.
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What is recommended after finding an elevated alpha-fetoprotein level? See details
under NTD
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- A directed system ultrasound scan to identify defects associated with an elevated
alpha-fetoprotein level should be performed between the 22nd and the 24th week.
It is also advisable to perform amniocentesis (funded by the Ministry of Health)
since this will allow both measurement of the alpha-fetoprotein level in the amniotic
fluid, and also examination of the fetus's chromosomes.
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- If the alpha-fetoprotein level in the amniotic fluid is found to be high, the fluid
is sent for further testing for a substance known as acetylcholine esterase. This
substance is secreted into the amniotic fluid only from the neural tube, so its
presence indicates a defect in the closure of the neural tube. Its absence leaves
the other differential diagnoses for elevated alpha-fetoprotein levels. These will
be discussed during genetic
counseling.
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