Amniotic fluid phospholipids. New predictive values of L/S and PG/S ratios

The lecithin/sphingomyelin (L/S) ratio after cold acetone precipitation is widely used to predict fetal lung maturity. The separation of saturated lecithin, the main component of surfactant, is the basis for using the precipitation procedure but there is still a controversy as to whether cold acetone precipitable lecithin can be equated with saturated lecithin. Following up a previous paper in which the effect of cold acetone precipitation on phospholipids of amniotic fluid was studied, the present work reports that non-precipitated L/S and phosphatidylglycerol/sphingomyelin (PG/S) ratios correlate well with the precipitated L/S ratio (r = 0.93, r = 0.84, n = 92). The predictive value of both non-precipitated L/S and PG/S ratios has been studied when a "positive" result predicts a precipitated L/S ratio > or = 2.0, and proposes a L/S ratio > or = 4.7 and a PG/S ratio > or = 0.8 to predict fetal lung maturity, when cold acetone precipitation step is omitted.