Analysis of phospholipids in human amniotic fluid by 31P NMR

A recently described solvent-reagent system for obtaining narrow linewidths in 31P NMR spectra of phospholipid extracts was applied to human amniotic fluid. Resolution of the major components was achieved by manipulating the solvent composition, and assignments were made by spiking samples with standard compounds. Spin-lattice relaxation times were determined and used to optimize data acquisition. NMR estimates of the phosphatidylcholine to sphingomyelin ratio for 33 patients were compared to those obtained by TLC densitometry, a common clinical assay for fetal pulmonary maturity. Estimates of the levels of phosphatidylglycerol and phosphatidylinositol could also be obtained from 31P NMR. High-resolution 31P NMR in this solvent-reagent system provides a relatively straightforward and reliable alternative method for assessing fetal pulmonary status by phospholipid quantitation in human amniotic fluid. The 31P NMR method has the advantage that it is sensitive to total, and not just unsaturated, phosphatidylcholine.