Prediction of RDS by amniotic fluid analysis: a comparison of the prognostic value of traditional and recent methods.

The determination of lecithin or even more the lecithin/sphingomyelin (L/S) ratio in amniotic fluid are both well established in the prediction of neonatal RDS. The immunological measurement of phosphatidylglycerol (PG) and the determination of the surfactant/albumin (S/A) ratio by fluorescence polarization (TDx FLMR) have recently been introduced for the detection of fetal lung maturity. In order to compare traditional versus recent methods L/S ratio and PG determination by one dimensional thin-layer chromatography, enzymatic analysis of lecithin, immunological determination of PG by Amniostat-FLMR and the fluorescence polarization of S/A-ratio by the TDx FLMR were all performed in 141 amniotic fluid samples of 122 patients. Only one out of 72 samples was false negative in the enzymatic lecithin determination (sensitivity 88%). All other methods have a sensitivity and a negative predictive value of 100%. The positive predictive values and the specificity varied between 22%-50% and 58%-87% respectively. The false positive rate, which is high for all methods, is lowest for the L/S ratio. This study demonstrates, that the recent methods are reasonable alternatives in all cases with a positive test. In clinical practice they have the advantage, that the result can be obtained in 15 minutes. If the test is predictive for lung immaturity the L/S ratio should be performed in addition to decrease the false positive rate before any clinical decision is made.