Assay of bacterial endotoxin (lipopolysaccharide) in human amniotic fluid: Potential usefulness in diagnosis and management of preterm labor

The long-range goal of our research is to determine whether the presence of bioactive agents of infection in amniotic fluid may serve as sensitive indexes of the existence of infection as the cause of preterm labor in a given pregnancy. The aim of this study was to explore the possibility that bacterial endotoxin (lipopolysaccharide) could be detected and quantified in amniotic fluid. In particular, we sought to ascertain (1) if amniotic fluid could be collected in a manner to prevent endotoxin contamination, (2) whether there were inhibitors of lipopolysaccharide in amniotic fluid, and (3) if Limulus amebocyte lysate-based assays could be used to identify and quantify lipopolysaccharide in this fluid. We found that the Limulus amebocyte lysate assays (gelation assay and chromophore generation assay) were useful in the qualitative and quantitative analysis of lipopolysaccharide in amniotic fluids. Lipopolysaccharide-mediated generation of chromophore in the presence of amniotic fluid was accelerated strikingly compared with that of lipopolysaccharide in endotoxin-free water. In three amniotic fluid samples obtained during preterm labor, lipopolysaccharide was detectable in aliquots of 1 to 10 μl by use of the gelation assay and lipopolysaccharide was quantifiable by use of chromophore generation assays. Two of these amniotic fluid samples were sterile as determined by bacteriologic examination; in the third sample, Fusobacterium species was identified. We suggest that these assays may be extremely useful in the identification of lipopolysaccharide in amniotic fluid. Indeed, lipopolysaccharide may serve as one marker of infection useful in establishing the cause of preterm labor.