Alpha-fetoprotein (AFP) Test

The Alpha-fetoprotein (AFP) test is a blood test that measures the level of alpha-fetoprotein, a protein produced by the liver and yolk sac of a fetus. The test is typically performed during pregnancy to screen for certain fetal abnormalities.

Purpose of the Test

The primary purpose of the AFP test is to identify pregnancies at increased risk for:

• Neural tube defects (NTDs), such as spina bifida and anencephaly
• Chromosomal abnormalities, such as Down syndrome and trisomy 18
• Fetal abdominal wall defects, such as omphalocele

How the Test is Performed

The AFP test involves a simple blood draw from the mother's vein. The blood sample is then sent to a laboratory for analysis.

Interpretation of Results

AFP levels are typically measured in terms of multiples of the median (MoM). A result is considered:

• Normal: 0.5-2.5 MoM
• Borderline: 2.5-3.5 MoM
• Elevated: above 3.5 MoM

An elevated AFP level may indicate an increased risk for certain fetal abnormalities, while a low AFP level may be associated with chromosomal abnormalities.

Limitations of the Test

The AFP test is not diagnostic, but rather a screening tool. A positive result does not necessarily mean that the fetus has a problem, and further testing, such as ultrasound or amniocentesis, may be necessary to confirm any potential issues.

Risk Factors and Considerations

Certain factors can affect AFP levels, including:

• Multiple pregnancy (twins, triplets, etc.)
• Fetal age and gestational age
• Matternal weight and ethnicity
• Certain medical conditions, such as liver disease or diabetes

Follow-up Testing

If the AFP test result is abnormal, follow-up testing may include:

• Ultrasound examination to evaluate fetal anatomy and growth
• Amniocentesis to analyze fetal cells for chromosomal abnormalities
• Chorionic villus sampling (CVS) to analyze placental tissue for chromosomal abnormalities

It is essential to discuss the results of the AFP test with a healthcare provider to determine the best course of action and any necessary follow-up testing.

Frequently Asked Questions (FAQs)

What is the Alpha-fetoprotein (AFP) test?
A blood test measuring alpha-fetoprotein levels in pregnant women.

Why is the AFP test performed?
To screen for potential fetal abnormalities and birth defects.

What does a high AFP level indicate?
Possibly neural tube defects or multiple pregnancy, but may also be false positive.

What does a low AFP level indicate?
Possibly Down syndrome or other chromosomal abnormalities, but may also be false negative.

Is the AFP test diagnostic?
No, it is a screening test, requiring follow-up testing for diagnosis.

When is the AFP test typically performed?
Between 15 and 20 weeks of pregnancy.

What are the risks associated with the AFP test?
Minimal, as it is a simple blood draw, but false results can cause unnecessary anxiety.

Can the AFP test detect all birth defects?
No, it has limitations and may not detect some abnormalities.

Are there any factors that can affect AFP levels?
Yes, such as multiple pregnancy, gestational age, and maternal weight.

What happens if the AFP test results are abnormal?
Further testing, such as ultrasound or amniocentesis, is usually recommended to confirm diagnosis.