Reactivity of amniotic fluid alpha-fetoprotein with concanavalin A-sepharose in pre-natal diagnosis of fetal malformations

Abstract

The proportion of concanavalin A-non-reactive alpha-fetoprotein was determined in 215 amniotic fluid samples from second trimester pregnancies. The median percentage for concanavalin A-non-binding alpha-fetoprotein was 35.5% at the 15th week and 32.2% at the 18th gestational week. Nineteen of the 23 pregnancies with various fetal malformations showed highly elevated total alpha-fetoprotein levels. In this group, the value for non-reactive alphafetoprotein was below the normal range in 12 out of 13 samples collected at 15–17 weeks of pregnancy and in four out of six samples at 18–19 weeks. Four pathological pregnancies had only moderately elevated total alpha-fetoprotein levels (5.3–7.9 SD above the mean) and two of these samples had a low percentage of the concanavalin A-non-binding fraction. The amniotic fluid alpha-fetoprotein concentration was between 3 and 5 SD and over 5 SD above the mean in four and seven normal pregnancies, respectively. The concanavalin A-fractionation classified correctly 10 out of these 11 cases. The results indicate that the determination of the proportion of concanavalin A-non-binding alpha-fetoprotein is a useful supplementary test to the total alpha-fetoprotein assay.

Key-words:

• alpha-fetoprotein test
• concanavalin A-chromatography
• congenital malformations
• early pregnancy