Mechanism of accumulation of amniotic fluid pigment in erythroblastosis fetalis

Abstract

Studies were performed to elucidate the mechanism of accumulation of amniotic fluid bilirubin pigments in erythroblastosis fetalis. Results revealed that unconjugated bilirubin in amniotic fluid is bound to albumin and that albumin averages 65 per cent of total amniotic fluid protein, even in the presence of fetal hydrops, where total protein is markedly elevated. Saturation of fetal albumin is well below the capacity of this protein to bind bilirubin and a concentration gradient exists between fetal plasma and amniotic fluid which appears to favor the transfer of bilirubin across partitioning membranes. In 3 cases, experimental elevation of amniotic fluid albumin content increased the bilirubin content of amniotic fluid. It is suggested, therefore, that the accumulation of bilirubin in amniotic fluid resembles the transplacental passage of bilirubin from fetus to mother and is dependent on the gradient of bilirubin-albumin complexes across the separatory tissues.