The beta-core fragment of chorionic gonadotropin is not complexed to macromolecules in amniotic fluid

A prior report claimed that amniotic fluid contains substantial quantities of beta-core fragment, a major degradation product of CG metabolism, complexed to macromolecules. In an attempt to confirm this finding, we measured beta-core fragment concentrations in 36 second- and 22 third-trimester amniotic fluid samples in a direct beta-core fragment RIA as well as a total CG RIA and found that all of the apparent immunoreactivity could be accounted for by the cross-reaction of CG and CG beta in the beta-core fragment RIA. Chromatography of concentrated pools of amniotic fluid or pregnancy serum failed to reveal a peak of CG immunoreactivity in the beta-core fragment elution area. However, chromatography after incubation of amniotic fluid or pregnancy serum with 3 mol/L ammonium thiocyanate resulted in a peak of apparent CG immunoreactivity in the area coinciding with the elution of ammonium thiocyanate and not purified beta-core fragment. The addition of ammonium thiocyanate to the CG RIA tubes resulted in apparent, but spurious, CG immunoreactivity. We conclude that amniotic fluid does not contain appreciable amounts of free or complexed beta-core fragment. We also were unable to confirm the presence of beta-core fragment complexed to macromolecules in pregnancy serum. Our results suggest that the previous studies that purported to demonstrate beta-core fragment-macromolecular complexes in amniotic fluid and pregnancy serum were reporting artifacts introduced by the ammonium thiocyanate used to dissociate beta-core fragment from the putative complex or the in vitro generation of beta-core fragment.