Measurement of alpha fetoprotein (AFP) levels in amniotic fluid has been used as a diagnostic tool for detection of neural tube defects (NTDs) in the fetus. AFP measurement in conjunction with ultrasonography yields a 90% NTD detection rate. The technique is recommended for use in pregnancies known to be at risk of NTDs and as a screening technique for use with 2nd-trimester amniocentesis. In recent years, maternal serum AFP assays have been used for NTD detection. The technique has promise as a diagnostic tool but is not recommended for routine maternal screening. Problems with maternal AFP screening are: 1) the large number of false positive results; 2) lack of general patient and physician education on the screening technique; 3) technical problems related to the assay; 4) inconsistency of assay results from 1 laboratory to another; and 5) the lack of established normal standards for the test.
