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How Alpha-fetoprotein Levels or the AFP Test Predicts Developmental Fetal Abnormalites in The Pregnant Mother

Updated on April 5, 2013

What is Alpha-fetoprotein

I wrote this research paper during my OB/GYN rotation in school. It describes what is Alpha-fetoprotein (AFP) and how it is used as a indicator for certain abnormalites within pregnant women or adult males, non pregnant woman and children. Keep in mind, the tests are NOT definitive, just an indicator that MIGHT point toward an abnomality, which will require further testing before anything is definite. So if you were curious and wanted to learn more about that AFP test you were recently given (perhaps in the OB/GYN office), read on!

Alpha-fetoprotein (AFP) is a glycoprotein that is also a hormone produced first by the yolk sac, then eventually by the liver of the fetus during pregnancy. Some other glycoproteins which are also hormones are the luteinizing hormone, thyroid - stimulating hormone and the Human chorionic gonadotropin hormone.

While glycoproteins serve many different functions such as a lubricant and protective agent in mucins, a transport molecule in transferrin (transport iron to cells) or as a hormone like Human chorionic gonadotropin, the true function for AFP is currently unknown. However differing AFP levels can be used as an important marker for the prenatal diagnosis of developmental abnormalities or as a biomarker for cancer or tumours within an adult male, non pregnant woman and children.

Sometimes AFP Levels May Be Inaccurate

The highest amount of AFP produced in a human body normally is by the fetus which eventually tapers to almost nil within a short time after birth. Indeed in a healthy male or non pregnant woman and child, the presence of AFP is extremely low to none. If there are elevated AFP levels detected in an adult male, non pregnant woman or child this indicates there might well be a cancer predominately of the stomach, ovaries, testicles, pancreas or liver.

The fetus excretes AFP into its urine which is eventually passed into the amniotic fluid, after which a small portion of the AFP passes through the placenta or membranes into the mother’s blood system. The AFP concentration is quite small in the maternal blood (this same concentration level within a non cancerous/ non-pregnant woman, would be considered high) compared to the fetal AFP concentration levels . With precise dating of the pregnancies, a baseline curve was developed for normal maternal AFP blood levels for different gestational ages. If the AFP levels detected are outside of the established baseline, it is suggestive of birth defects for the fetus. Of course an elevated AFP (higher than the normal curve) can also occur and still be normal, such as multiple gestations, too little amniotic fluid or even an incorrect dating of the pregnancy all of which will elevate the AFP levels.

Abnormalities a High AFP Level Might Indicate

During pregnancy, an elevated AFP level in the maternal blood can be indicative of neural tube defects in the fetus which include spina bifida and anencephaly. Other notable elevated AFP problems are liver disease, brittle bone disease, defects in the abdominal wall, urinary tract defects, duodenal atresia, omphalocele, tetralogy of Fallot, and more. An abnormally low AFP level might indicate that the fetus is at risk for having Trisomy 21 or Down syndrome, or there may have been fetal demise or the mother is overweight.

The AFP test or maternal serum AFP (MSAFP) measures the amount of AFP in the mother’s blood during pregnancy and usually done starting week 16. It is important to note that it is a screening test and not definitive by itself which means it is used to predict the probability of a serious birth defect but cannot define what kind of defect it is if any or in other words the test does not diagnose an issue, it only tells us further testing should be done. The screen test results dictate what type of test we might undertake next such as an ultrasound (check nuchal fold translucency for possible Down Syndrome) or amniocentesis (an accurate indicator for Down Syndrome).

What Some Other Screening Tests Look For

Besides the standard AFP test, there are 3 more tests which incorporate ATP, that aim for higher accuracies for detecting problems by testing for other substances or hormones, rather than just testing the ATP levels alone. They are the triple screen, quad screen and the penta test.

The triple screen measures the ATP levels and also beta-hCG and unconjugated estriol which look for additional genetic issues. The quad screen checks for the same things as the triple screen and in addition, checks the levels of the hormone inhibin A, which is a marker connected with Down Syndrome.

The penta test looks for the same four substances as the quad screen and in addition, checks for Invasive Trophoblast Antigen (ITA) or hyperglycosylated hCG which is another marker for Down Syndrome.

All these tests are generally between 16 and 20 weeks.

In conclusion it is important to remember that all of these tests are meant to screen for certain diseases and by itself, is not conclusive of anything. If you have any concerns certainly ask your doctor, I am sure he/she will be more than happy to assist you. Thanks for reading!

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