Spectral absorption curves were plotted on amniotic fluid specimens from 38 Rhsensitized patients and one ABO-sensitized patient. Height of the 450-mμ peak gives reliable prediction of the severity of the hemolytic process of the fetus: peaks of 5 units or less were associated with infants who showed only minimal or no evidence of hemolytic disease; peaks greater than 5 units were associated with increasing hemolytic disease. Amniocentesis was found to be a safe valuable prenatal procedure, an aid to the physician in determining which patients require early delivery (thereby reducing mortality from erythroblastosis) and which can go to term (thereby eliminating complications which might arise from early induction of labor).
Lewis F, Schulman H, Hayashi TT. Spectrophotometric Analysis of Amniotic Fluid in Erythroblastosis Fetalis. JAMA. 1964;190(3):195-198. doi:10.1001/jama.1964.03070160019004