The Alpha-Fetoprotein (AFP) test is a common screening tool offered during pregnancy. It primarily helps assess the risk of certain birth defects and genetic conditions in the developing baby. While it serves as an important screening measure, an elevated AFP result does not automatically signify a problem. Instead, it often points to the need for further investigation, as these screening tests can sometimes produce what is known as a “false positive” result.
Understanding a False Positive
A “false positive” in an AFP test means the test indicates higher-than-expected levels, suggesting a potential risk even though the condition is not present. The AFP test is a screening, not a diagnostic, tool; it identifies pregnancies that may have a higher risk but does not confirm a diagnosis. An abnormal result flags the need for closer examination, not necessarily an actual problem.
Common Reasons for Elevated AFP
Several factors can lead to an elevated AFP level, resulting in a false positive. One of the most frequent reasons is inaccurate gestational dating. AFP levels naturally change throughout pregnancy, so if the estimated due date is incorrect, the AFP level may appear abnormal when it is actually appropriate for the true gestational age. For instance, if a pregnancy is further along than initially believed, AFP levels will naturally be higher. Studies indicate that misinterpretation of AFP results due to incorrect gestational dating occurs in a notable percentage of screened women.
Multiple pregnancies are another common cause of elevated AFP levels. Each developing baby produces AFP, so carrying twins, triplets, or more naturally leads to higher concentrations of the protein in the mother’s blood. The average AFP levels in twin pregnancies can be double those in singleton pregnancies. This elevation is expected and accounted for when interpreting results for multifetal pregnancies.
Certain maternal health conditions can also influence AFP levels. Liver conditions in the mother, such as hepatitis or cirrhosis, can cause elevated AFP. Additionally, some less common factors can contribute, including maternal weight, with lighter women often having higher AFP levels due to a more concentrated blood volume. While historically some interpretations of AFP tests included race-based adjustments, recent research suggests no significant differences in AFP levels between Black and non-Black patients when adjusted for gestational age and maternal weight, indicating such adjustments may be unnecessary.
Placental issues can sometimes lead to elevated AFP. Conditions like placental abruption or other abnormalities can cause AFP to rise, as increased permeability allows more fetal AFP to cross into the maternal bloodstream. Though rare, laboratory or testing errors can also contribute to an inaccurate result.
Next Steps After an Elevated Result
Following an elevated AFP result, healthcare providers typically recommend further evaluation. The initial step often involves a detailed ultrasound examination to confirm gestational age, check for multiple pregnancies, and look for any visible anomalies. This can clarify if the elevated AFP is due to incorrect dating or the presence of more than one fetus.
If the initial ultrasound does not provide a clear explanation, more advanced diagnostic procedures might be offered. These can include a targeted fetal ultrasound for a more detailed view of the baby’s anatomy, or amniocentesis. Amniocentesis involves taking a small sample of amniotic fluid for analysis, providing a more definitive diagnosis.
Throughout this process, discuss all results and options with a healthcare provider or genetic counselor. They offer personalized guidance, interpreting findings and helping families make informed decisions. Many elevated AFP results ultimately turn out to be false positives, with most pregnancies resulting in healthy babies.