The Alpha-Fetoprotein (AFP) test is a common prenatal screening. It identifies pregnancies that may be at a higher risk for certain conditions, rather than definitively diagnosing them.
Understanding the Alpha-Fetoprotein Test
Alpha-fetoprotein (AFP) is a protein produced by the developing baby, primarily by the fetal liver and yolk sac. During pregnancy, some of this protein crosses the placenta and enters the pregnant person’s bloodstream. The AFP test, often referred to as maternal serum AFP (MSAFP), measures the level of this protein in the mother’s blood.
The procedure for the AFP test involves a routine blood draw from a vein in the arm. The sample is then sent to a laboratory for analysis, with results typically available within one to two weeks. While commonly associated with pregnancy, AFP can also be measured in non-pregnant individuals to help diagnose certain cancers, especially liver cancer.
Optimal Timing for AFP Screening
The timing of the AFP test is important for obtaining accurate results. Healthcare providers recommend conducting the AFP test between 15 and 20 weeks of pregnancy. The window from 16 to 18 weeks of gestation is considered ideal for this screening.
This specific timeframe is important because AFP levels naturally change throughout pregnancy. Accurate dating of the pregnancy is essential for proper interpretation of the test results. Performing the test too early or too late can lead to less reliable outcomes, including false positives or false negatives.
Why the AFP Test is Performed
The primary purpose of the AFP test during pregnancy is to screen for certain birth defects and genetic conditions. It identifies pregnancies with an increased risk of neural tube defects, such as spina bifida and anencephaly. Neural tube defects occur when the baby’s brain, spine, or spinal cord do not form properly.
The test is also part of a broader screening for chromosomal abnormalities like Down syndrome (Trisomy 21) and Edwards syndrome (Trisomy 18). AFP levels are often combined with other markers in a multiple marker screen (e.g., triple or quad screen) for a more comprehensive risk assessment.
Interpreting Results and Next Steps
Abnormal AFP levels, whether higher or lower than expected, do not automatically indicate a problem with the baby. Common reasons for elevated AFP levels include an incorrect estimation of the due date or carrying multiple babies, such as twins. Levels can also be influenced by factors like maternal weight or the presence of gestational diabetes.
If an abnormal result occurs, it signifies a need for further investigation rather than a diagnosis. The next step often involves a detailed ultrasound to confirm gestational age, check for multiple pregnancies, and examine the baby for physical anomalies. In some cases, additional diagnostic tests like amniocentesis may be recommended for a definitive diagnosis. Genetic counseling may also be offered to help parents understand the results and their options.