[Concanavalin A reactivity of alpha-fetoprotein in the amniotic fluid in autosomal trisomies of the fetus].

Fetal trisomies 21 and 18 have been found to be associated with low maternal serum alpha-fetoprotein values in the second trimester of pregnancy. The concanavalin A reactivity of amniotic fluid alpha-fetoprotein of 35 fetuses with trisomy 21 and 7 fetuses with trisomy 18 between the 16th and 24th week's gestation has a normal pattern of distribution. In 7 cases of autosomal trisomies in association with other malformations (neural tube defect, omphalocele, non-immune hydrops fetalis), the percentage of the fraction without affinity for concanavalin A was significantly lowered. These results do not support the hypothesis of a qualitatively altered fetal production of alpha-fetoprotein as a cause of lowered maternal serum alpha-fetoprotein levels in cases of fetal autosomal trisomy.