Zinc and alpha-fetoprotein in amniotic fluid from early pregnancies with fetal malformations.

Zinc and alpha-fetoprotein concentrations were quantitated in second-trimester amniotic fluid from 111 normal pregnancies and 29 pregnancies with various fetal malformations. The zinc level varied between 0.3 and 4.0 mumol/L (median 1.3) in the normal samples and between 1.8 and 17.9 mumol/L (median 5.0) in cases with malformations. The level was above 2.5 times the normal median in 23 of the 29 (79%) gestations with the malformations. Amniotic fluid zinc and alpha-fetoprotein levels showed a positive correlation (r = 0.78), and the alpha-fetoprotein level was elevated in all gestations with fetal disorders and elevated zinc levels, as well as in five of the six cases with fetal defects but normal zinc concentrations. The elevation of zinc was more marked than that of alpha-fetoprotein in three cases of fetal malformations. Five samples were false positive on alpha-fetoprotein assay but contained normal zinc levels. Removal of alpha-fetoprotein from amniotic fluid had no effect on the zinc concentration, indicating that zinc is not bound to amniotic fluid alpha-fetoprotein.