The alphafetoprotein test is a simple non-invasive blood test that is used to detect fetal abnormalities during the early stages of pregnancy.
Alphafetoprotein is a compound known as glycoprotein. It is manufactured first by the embryo's yolk sacThe structure that is attached to the embryo and provides initial nourishment until about the 7th week when it disappears.
The cells of the yolk sac (extraembryonic mesoderm) differentiate to develop early blood cells including the endothelium, primitive plasma and hemoglobin.
Visit our comprehensive glossary for more pregnancy terms and definitions., then later by the fetal liver. Alphafetoprotein is an important carrier of molecules in the fetal bloodstream.
Between week sixteen and week twenty four the levels of alphafetoprotein double every five weeks and traces appear in the mother's bloodstream. When an alphafetoprotein test is performed a blood sample is taken from the mother and levels of alphafetoprotein are measured. Results can show low, normal or high levels of alphafetoprotein present in the blood.
Alphafetoprotein testing is voluntary for most women, although it is required in some states such as California and New York. Many US doctors consider alphafetoprotein testing a routine part of prenatal care and you can expect to be offered one AFP screen during your pregnancy.
Alphafetoprotein testing by itself does not provide any conclusive results about the development of the fetus. It does indicate whether more specific testing is required and may protect the doctor from accusations of overlooking certain developments in the growth of the fetus.
There are few, if any, risks associated with this test.
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The alphafetoprotein test may be performed any time between week fourteen and week twenty. The most accurate results are achieved when it is done between week sixteen and week eighteen. Results from the blood test are returned from the laboratory within two or three days.
Results of the alphafetoprotein test will reveal low, normal or high levels of the protein in the mother's blood. If the levels of alphafetoprotein are low, it may indicate the presence of chromosomal abnormalities such as Down's syndromeA congenital abnormality in which the baby is born mentally retarded, with an average IQ of 50 - 60 and with physical deformation of the face (low set ears, sloping forehead, mongoloid eyes), and shortness of stature.
Downs syndrome is caused by an extra chromosome 21 present in the G group. In a small percentage of cases it can be caused by the switching of chromosomes 14 or15 in the D group or chromosome 21 or 22.
Down's syndrome occurs in about 1 in 650 births, and is more commonly associated with children of mother's over the age of 35. Incidence in children of mothers over the age of 40 can be as high as 1 in 80.
Down's syndrome can be detected prenatally through amniocentesis. The mortality rate is high within the first few years. Down's syndrome is also known as mongolizm, trisomy 21 or trisomy G syndrome.
Visit our comprehensive glossary for more pregnancy terms and definitions.. A repeat test is usually indicated, followed by an ultrasound and amniocentesis which will be necessary to confirm the test. The alphafetoprotein test can predict the presence of Down's syndrome about sixty five percent (13 in 20) cases.
If the test returns high levels of alphafetoprotein it may indicate the presence of certain birth defects. High levels of alphafetoprotein are consistent with neural tube defectsAny of a group of congenital malformations that involve the skull and the spinal column. Most commonly it involves the failure of the neural tube to close properly during embryonic development.
High levels of alphafetoprotein in the amniotic fluid can reveal potential problems prenatally, and the fetus can be scanned using ultrasound. Immediate surgical repair is required.
Visit our comprehensive glossary for more pregnancy terms and definitions. such as anencephalyA congenital defect in which the brain and spinal cord are absent, the cranium remains open and the vertebral canal stays grooved.
Anencephalic defects are transmitted genetically and can be detected early in the pregnancy by amniocentesis and ultrasonic testing. Anencephaly is not compatible with life. See also, neural tube defect.
Visit our comprehensive glossary for more pregnancy terms and definitions., a condition in which part of the fetal skull is missing and is not compatible with life. High levels of protein leaking out of a defective spinal cord may also indicate spina bifidaA relatively common birth defect in which the spine fails to form properly leaving the spinal cord exposed. Spina bifida can result in mental disability and partial paralysis. Also called spinal dysraphia.
Visit our comprehensive glossary for more pregnancy terms and definitions.. The opening can often be repaired, although it may result in paralysis below the waist and will often lead to the development of hydrocephalyA congenital abnormality in which excessive fluid collects on the brain enlarging the skull. Surgical treatment with a survival rate greater than 80% involves a combination of procedures including correction of the ventricular obstruction, reduction of the production of cerbralspinal fluid and the installation of shunts to drain excess fluid to the right atrium of the heart or peritoneal cavity.
Visit our comprehensive glossary for more pregnancy terms and definitions..
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A high level of alphafetoprotein is not always cause for alarm. Of the five percent (50 in 1000) alphafetoprotein tests that return high levels only two (0.2%) will have neural tube defectsAny of a group of congenital malformations that involve the skull and the spinal column. Most commonly it involves the failure of the neural tube to close properly during embryonic development.
High levels of alphafetoprotein in the amniotic fluid can reveal potential problems prenatally, and the fetus can be scanned using ultrasound. Immediate surgical repair is required.
Visit our comprehensive glossary for more pregnancy terms and definitions.. The remaining forty eight may be the result of carrying twins, an inaccurately dated pregnancy, other defects or unknown reasons. A subsequent test will be performed to confirm the results and if they are still positive an ultrasound will be provided to confirm the presence of twins or the age of the fetus.
The alphafetoprotein test is subject to many false positive results. A positive test is always confirmed with an ultrasound, which is used to confirm the presence of life, the gestational age of the fetus or the presence of twins. If the age of the fetus is older than previously thought, then the results of the alphafetoprotein test are recalculated to adjust for the date. A second alphafetoprotein test is performed and if the results still show positive, then amniocentesis will be performed to confirm or rule out the diagnosis.
There are false negatives associated with the alphafetoprotein test and if the results are normal it does not always mean that abnormalities are not present.
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