Diagnostic use of meternal serum alpha-fetoprotein levels.

Alpha-fetoprotein (AFP) levels in human maternal serum were elevated in 14 patients when measured by a radioimmunoassay. In 8 patients the elveated serum levels of AFP correlated with increased concentration of AFP in amiotic fluid and were diagnostic of fetal defects. The elevated AFP levels in the remaining 6 patients were shown to be the result of fetomaternal transfusion from either amniocentesis or natural causes. Serum samples drawn after amniocentesis through an anterior placenta may show false-positive elevations. The use of both maternal serum and amniotic fluid samples in pregnancies at high risk for neural tube defects can decrease the risk of diagnostic errors due to mistakes in gestational datind and may increase the diagnostic sensitivity of amniocentesis.