Methods for extracting phospholipids from human amniotic fluid compared.

Phospholipids were extracted from human amniotic fluid by various procedures, including the two most commonly applied to amniotic fluid for evaluation of fetal lung maturity. We find that the yield of phospholipid is greatly procedure dependent. This should be taken into account when one is considering the various reported methods of evaluating fetal lung maturity, because in some of them phospholipid data are expressed in terms of absolute concentration in the amniotic fluid. There were also significant differences in phospholipid composition in extracts prepared by the various procedures, but in general these were not large enough to influence evaluation of fetal lung maturity by methods in which phospholipid data are expressed in relative terms, as ratios or percentages--e.g., in the lecithin/sphingomyelin ratio and "lung profile" procedures. In the extraction method originally recommended for determination of the lecithin/sphingomyelin ratio, both the yield and composition of phospholipid depend on the extent of mixing.