AFP Test (Alpha-Fetoprotein) : Purpose, Procedure, Risks, and Benefits

Overview

An alpha-fetoprotein (AFP) test is a blood test to measure the amount of AFP protein present in the expectant mother’s blood. The test is a part of the triple screening tests, typically conducted in the second trimester of pregnancy. However, the test also has some significance in non-pregnant adults.

Unborn babies typically produce alpha-fetoprotein (AFP), which is present in the mother’s blood. If doctors check the level of AFP in a pregnant woman, it can indicate if the baby would suffer neural tube defects, such as spina bifida. Additionally, a high-quality second-trimester ultrasound can detect more neural tube defects than an AFP test alone. 

This blog comprehensively explains an AFP test, its purpose, procedure, risks, benefits and results.

What is an AFP test?

An AFP test is a blood test that doctors use to measure the amount of AFP in a pregnant woman’s blood. Typically, it is part of a series of tests known as a triple screen, or quad screening that doctors perform in the second trimester of pregnancy. 

An unborn baby’s yolk sac, GI (gastrointestinal) tract, and liver produce AFP. The protein circulates through the fetal and maternal blood. Women who are not pregnant typically have low levels of AFP in their blood. However, higher levels of AFP in women who are not pregnant point out specific types of liver disease.

Why do women require an AFP test?

The test is a routine screening test recommended for expectant mother in the gestational age of 14 to 22 weeks of pregnancy. It is vital to note that the AFP test is the most accurate between 16 to 18 week; therefore it is important for the pregnant woman to know the exact date of conception. The test is a part of a quad screen test that helps in testing the levels of:

• Human chorionic gonadotropin (hCG) hormone
• Estriol, a hormone produced by the placenta and the baby’s liver
• Inhibin A, another hormone produced by the placenta

Doctors determine the chances of the unborn baby developing genetic birth defects based on the quad screen results, the age and ethnicity of the mother. Defects detected may include, neural tube defects such as spina bifida, and chromosomal abnormalities, such as down syndrome. The test results also aid in determining if the expectant mother needs further tests to check for genetic conditions.  However, a positive test result may not mean that the unborn child has a birth defect. The test is vital for women at a higher risk of giving birth to children with birth defects. Women:

• Who are 35 and older
• With a family history of congenital defects
• Using harmful medications or drugs during pregnancies
• With diabetes

The test also helps women who are not pregnant to diagnose and monitor certain liver conditions including liver cancer, cirrhosis, and hepatitis. It also detects cancers such as:

• Testes
• Ovaries
• Biliary tract
• Stomach 
• Pancreas

How is an AFP test performed?

Doctors must take the pregnant woman’s blood for an AFP test. It is an outpatient procedure, is generally performed at a diagnostic lab.The doctor uses a tiny needle to draw blood from a vein, generally in the woman’s arm or hand. A laboratory specialist analyses the sample and gives the result .

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What happens after an AFP test?

Sometimes women can get a false positive which means the test indicates an abnormality even when everything is normal. The doctor likely verifies the results with other tests to ensure the baby is healthy.

When the woman’s AFP is too high or low, the doctor can suggest further testing, including an ultrasound, to confirm the duration of the pregnancy and the number of babies. They also look out for congenital disabilities.

When the results are abnormal, the doctor can ask for a more invasive test, such as amniocentesis, in which the doctor uses a long, thin needle to draw a small amount of amniotic fluid from around the fetus for lab analysis.

What risks are associated with an AFP test?

An AFP test significantly carries fewer risks. Women may faint or have some soreness or pain at the site where doctors pierce the skin. There is also a minor risk of excessive bleeding or hematoma if blood accumulates beneath the skin and infection at the injection site doctors penetrate the skin.

What are the benefits of an AFP test?

An AFP test helps doctors determine if women are at a greater risk of having a baby with a congenital disability. 

Conclusion

Doctors perform an AFP test to check the alpha-fetoprotein level in a woman’s blood during pregnancy. An AFP test also examines the baby’s risk of having some genetic issues and congenital disabilities and is generally done between the 15th and 20th week of pregnancy. Depending on the results, the doctor can recommend further testing.

Frequently Asked Questions (FAQs)

1. Do women require any preparation for the AFP test?

No, women do not require any special preparation for the AFP test.

2. What do the results of an AFP test mean?

A normal or negative test typically means the baby does not have genetic abnormalities linked to the neural tube. 

A positive test with a high AFP indicates a congenital disability such as spina bifida. A positive test with low AFP can indicate health problems such as Down syndrome or Edwards syndrome.

High AFP may also indicate that the pregnancy has progressed faster than women know. AFP peaks at 28-32 weeks and begins to decline. High levels of AFP can also occur in twin pregnancies (since two babies produce more AFP than one). The other factors influencing the result can include the woman’s race, weight, and diabetes.

Women must not worry if the AFP results are abnormal since it only reveals that women can be at risk of an abnormal pregnancy.

3. What are the other tests that the doctor can suggest?

Doctors perform AFP tests as part of a group of prenatal tests known as multiple markers or triple screen tests. Sometimes, they can ask for a fourth test known as an inhibin A test. If women are at a greater risk of having a baby with certain congenital disabilities, the doctor can also recommend prenatal cell-free DNA (cfDNA) screening. Doctors can do this blood test as early as the 10th week of pregnancy to check if the baby is at a greater risk of having Down syndrome or other genetic disorders.