The origin of plasma proteins in human amniotic fluid: the significance of alpha 1-antichymotrypsin complexes.

12 proteins were studied in serum and amniotic fluid from 20 women in late pregnancy by two-dimensional immunoelectrophoresis. A close inverse relationship was observed between the amniotic fluid/serum concentration ratios of 11 proteins and their Stokes radii. These proteins enter the liquor from the maternal blood by molecular filtration. The concentration of alpha 1-antichymotrypsin in amniotic fluid was often higher than expected and the protein was often partially complexed. alpha 1-Antichymotrypsin is probably not actively secreted into amniotic fluid but may be selectively retained after complexing.