Which of the following is a limitation of an alpha-fetoprotein (AFP) test?

The alpha-fetoprotein (AFP) test is primarily used as a screening tool during pregnancy to assess the risk of certain congenital conditions. One of the known limitations of the AFP test is that it does not detect all neural tube defects. While an elevated level of AFP may indicate the possibility of a neural tube defect, it is not definitive and can produce false-negative results. This means that some cases can go undetected, leading to a false sense of security if the test result is normal.

In contrast, the test has limitations in its specificity and sensitivity for other conditions, which can be misunderstood in the context of the options provided. For example, while it can indicate a risk for Down syndrome, it is not designed to detect it reliably; instead, other tests are preferred for that purpose. The effectiveness of the AFP test is also influenced by the timing during the pregnancy, usually providing the best sensitivity around 16 to 20 weeks, rather than later in the pregnancy. After 30 weeks, it is not considered a reliable marker, as the levels of AFP can fluctuate due to normal changes related to fetal growth and development.

Thus, the key limitation being identified here is that the AFP test does not detect all neural tube defects, making it important