Comparison of lecithin: sphingomyelin ratio, fluorescence polarization, and phosphatidylglycerol in the amniotic fluid in the prediction of respiratory distress syndrome.

The significance of the lecithin sphingomyelin (L:S) ratio as a determining factor in fetal lung maturity is well established. An L:S ratio of greater than 2.0 to 2.5 is indicative of fetal lung maturity in most assays. The fluorescence polarization method (fluorescence polarization less than 0.320) has been associated with fetal lung maturity. The presence of phosphatidylglycerol in amniotic fluid has been related to fetal lung maturity and the absence of respiratory distress syndrome. Amniotic fluid samples from 235 amniocentesis procedures and vaginal pool collection at varying gestational ages were analyzed for L:S ratio, fluorescence polarization, and phosphatidylglycerol. All samples with meconium or hemolyzed blood contamination and selected complications of pregnancy were removed from the study. A positive result will predict the absence of respiratory distress syndrome, and a negative result will predict the presence of respiratory distress syndrome. Correlation of L:S ratio, fluorescence polarization, and phosphatidylglycerol were favorable. False-positive results in three (3.3%) fluorescence polarization samples were noted, whereas there were none (0%) in the L:S ratio sample and one (1%) in the phosphatidylglycerol sample. Twenty-four (77.4%), 28 (73.7%), and 37 (77%) were the number of false-negatives in the fluorescent polarization, L:S ratio, and phosphatidylglycerol samples. Fluorescence polarization, L:S ratio, and presence of phosphatidylglycerol compare favorably as fetal lung maturity tests. The prediction of respiratory distress syndrome is as sensitive with the three modalities. The specificity and the predictive value of a positive test is more favorable with L:S ratio and phosphatidylglycerol.