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Alpha-Fetoprotein (AFP) in Blood

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In pregnant women, the amount of AFP gradually rises starting in the 14th week of pregnancy. It continues to rise until a month or two before giving birth, then it slowly decreases. Values are generally slightly higher for black women than they are for white women. Values are slightly lower for Asian women than they are for white women. An accurate estimate of the age of the baby is needed to understand the AFP value correctly.

The normal range of AFP values is adjusted for each woman's age, weight, and race; whether she has diabetes that needs injections of insulin; and the age of her baby (gestational age). If the age of the baby is changed after an ultrasound, the AFP must then be adjusted as well. Each woman and her doctor need to look at the range of AFP values that is normal for her when she has an AFP test.

High values

  • In a pregnant woman, high alpha-fetoprotein values can mean:
    • The age (gestational age) of the baby is wrong.
    • The woman is pregnant with more than one baby, such as twins or triplets.
    • The baby has a neural tube defect.
    • The baby's intestines or other abdominal organs are outside the body (called an abdominal wall defect or omphalocele). Surgery after birth will be needed to correct the problem.
    • The baby is not alive.
  • In a nonpregnant adult, high alpha-fetoprotein values can mean:

Low values

In a pregnant woman, a low level of alpha-fetoprotein can mean:

  • The age (gestational age) of the baby is wrong.
  • The baby may have Down syndrome.

In a nonpregnant adult, alpha-fetoprotein is not normally present.

What Affects the Test

Things that may affect the results of your test include:

  • If there is more than one baby (fetus). This increases the level of AFP in the blood.
  • If you have gestational diabetes.
  • If you smoke. This increases the level of AFP in the blood.
  • If you had a medical test that used radioactive tracers in the past 2 weeks.

WebMD Medical Reference from Healthwise

Last Updated: April 04, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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