Comparison of amniotic fluid alpha-fetoprotein reactivity to Lens culinaris agglutinin and concanavalin A in crossed-affinity immunoelectrophoresis: ancillary tests in the prenatal diagnosis of severe fetal malformations.

Crossed-affinity immunoelectrophoresis of alpha-fetoprotein in amniotic fluid from 135 normal and 39 abnormal pregnancies (mainly neural-tube defects) was performed with a lectin, agglutinin from Lens culinaris. Results were compared with findings reported for another lectin, concanavalin A. Three fractions of alpha-fetoprotein were obtained by reaction with Lens culinaris agglutinin. The most weakly reactive fraction correlated strongly with the concanavalin A nonreactive fraction. With both lectins, significantly lower concentrations of these fractions were found in all samples from abnormal pregnancies than in those from normal pregnancies. In eight cases with a fetal abnormality the total alpha-fetoprotein concentrations were below the lower limit for abnormal samples. All eight samples revealed fractions weakly reactive with Lens culinaris agglutinin below the lower 0.1% limit for normal samples; seven of these samples had fractions nonreactive with concanavalin A below this limit. Although a decrease in the two described fractions in normal pregnancies was found with increasing gestational age, we find either method to be valuable as an ancillary test in the prenatal diagnosis of fetal neural-tube defects and other malformations.