Determination of Lecithin–Sphingomyelin Ratio in Amniotic Fluid

Modifications have been incorporated in the method of Gluck and others for determining the lecithin–sphingomyelin ratio (L/S) in amniotic fluid. After thin-layer chromatography in chloroform:methanol:water, 12:5:1, the phospholipids are visualized by phosphomolybdic acid reagent. The untoward effects of storage, at room temperature, on the stability of L/S and the effects of amniotic fluid contamination with meconium or plasma on the L/S ratio have been investigated. In the followup of 41 pregnancies, low lecithin–sphingomyelin ratios, < 1.0, were confirmed before week 29, correctly predicting the development of respiratory distress syndrome in the premature newborn. In pregnancy of unknown duration or near term, low L/S values oblige one to maintain pregnancy until repeated sampling confirms fetal lung maturity.