Amniotic fluid fluorescence polarization value as a predictor of respiratory distress syndrome

Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene in amniotic fluid lipid aggregates was measured to determine the ability of this technique to prospectively predict respiratory distress syndrome. Prior retrospective studies have shown that an FP value of less than or equal to 0.336 correlated best with a lecithin to sphingomyelin ratio of greater than 2.0. Fluorescence polarization values of amniotic fluid samples obtained within 48 hours of birth from 161 pregnancies were correlated with neonatal outcome. Samples from 149 pregnancies had FP values of less than or equal to 0.336 and samples from 12 pregnancies had FP values of greater than or equal to 0.336. No infants delivered from the former group developed RDS and eight of 12 infants from the latter group developed RDS (P less than 0.001). In the entire population the test had a sensitivity of 100% and a specificity of 97%. When 37 infants with birth weights less than 2,500 gm were studied, the FP value remained a highly reliable predictor of the infant at risk for developing RDS (P less than 0.001). In this subset the test had a sensitivity of 100% and a specificity of 90%. L-S ratios were performed on 96 samples and the results correlated well with FP values (P less than 0.001). We conclude that the amniotic fluid FP value is a reliable index of fetal lung maturity and the risk for developing RDS. The FP value also has specific technical and diagnostic advantages over the L-S ratio.