Amniotic fluid lecithin, phosphatidylglycerol, L/S ratio, and foam stability test in predicting respiratory distress in the newborn.

Amniotic fluid phospholipids (lecithin, sphingomyelin, phosphatidylglycerol) were extracted and separated by the method of Gluck and associates. In addition, these lipids were quantified against standards that were concurrently developed in three adjacent thin layer chromatography (TLC) channels. A log-log transformation of the reflectance and concentration values provided rectilinear plots for quantification. A foam stability assay (FS) of 0.48 or greater was associated with high values of L/S ratio and lecithin concentration, and values of 0.44 or less almost always were associated with low values. Lecithin values of 12 micrograms/mL or more were associated with L/ S ratios of 2.0 or greater. Phosphatidylglycerol was detected consistently only when lecithin levels were 40 micrograms/mL or greater and L/S ratios 4.0 or greater. Case reviews indicated that: (1) FS test of 0.48 almost always was associated with pulmonary maturity in the newborn; (2) that a pulmonary maturity index combining the lecithin concentration and L/S ratio was a better predictor of pulmonary maturity in the newborn then either one alone; (3) that phosphatidylglycerol added little to this discrimination; and (4) that these assays showed no significant interpretative differences between diabetic and non-diabetic mothers.