Alpha-fetoprotein concanavalin A-binding variants in the diagnosis of neural tube defects and other communicating fetal abnormalities

We have extended our initial observations (Smith et al., 1979) on the use of determining the alpha-fetoprotein (AFP) concanavalin A-binding variant patterns in amniotic fluid for the detection of certain fetal malformations. We report here our complete series of amniotic fluids between 14 and 36 weeks of gestation from 52 normal pregnancies and 28 abnormal pregnancies including anencephaly, open spina bifida, Turner's syndrome, omphalocele, osteogenesis imperfecta congenita, meningo-myelocele, meningocele, spinal cysts, spontaneous abortion and fetal death. The percentage of the total amniotic fluid AFP which was not reactive with concanavalin A was significantly lower in the presence of a communicating fetal abnormality (mean = 4.8%, P<0.001), one in which the fetal/amniotic fluid barrier is defective, than in the presence of a normal fetus (mean = 24.7%) or of a non-communicating fetal abnormality. We applied the concanavalin A-binding assay to two of the above amniotic fluids from pregnancies in progress and correctly classified the gestations as abnormal. Our results indicate that measurement of the percentage of concanavalin A-non-reactive amniotic fluid AFP is a valuable adjunct in the diagnosis of a communicating fetal abnormality, especially when the elevation of amniotic fluid AFP concentration is equivocal (between 2 and 5 S.D. above the mean), when gestational aging is uncertain or when the total amniotic fluid AFP concentration and ultrasonographic data are inconsistent.