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.

Phospholipid surface tension: the diagnostic utility of amniotic fluid and its lipid extract, an analysis of the value of precipitation with cold acetone.

In prevention of the respiratory distress syndrome (RDS), measurements of surface tension values (a biophysical property) of amniotic-fluid samples are correlated with their lecithin/sphingomyelin (L/S) ratios (a biochemical property). According to some authors, precipitation of phospholipid with cold acetone is essential for determining the L/S ratio, because it separates surfactant and nonsurfactant phospholipidic fractions. Here we report the first study of the ability of three amniotic-fluid components to decrease surface tension: The complete lipid extract (without precipitation), and the fractions precipitated and (or) remaining soluble after addition of cold acetone. Addition of increasing aliquots of lipid extracts to these three samples showed that: (a) measurement of surface tension rapidly and reliably indicates fetal lung maturity, and (b) both precipitated and soluble phospholipid fractions decrease surface tension similarly, making it unlikely that the precipitation step in fact separates surfactant and nonsurfactant material.