Combined enzymatic assay of phosphatidylglycerol and phosphatidylcholine in amniotic fluid

Abstract

We present here a combined, quantitative enzymatic procedure for determining amniotic fluid phosphatidylglycerol and phosphatidylcholine and relate these findings to the assessment of fetal lung maturity. Under the assay conditions described phospholipase C specifically hydrolyses phosphatidylglycerol (PG) and phosphatidylcholine (PC) but not sphingomyelin, precluding the need for removal of sphingomyelin prior to analysis. Solvent extraction of the phospholipids from the amniotic fluid is, however, employed to avoid spurious elevation of PG and PC results by endogenous glycerol and choline. Of 45 amniocentesis fluids examined, 28 yielded detectable PG concentrations (> 0.5 μmol/l) and all but three of these exhibited PC concentrations in excess of 10 μmol/l. One case of respiratory distress occurred in an infant of 29 wk gestation with severe intrauterine growth retardation. Of the remaining 17 fluids in which PG was undetected enzymatically (⩽ 0.5 μmol/l), 14 also contained PC concentrations ⩽ 10 μmol/l and all six cases of true respiratory distress syndrome came from within this sub-group. Strong correlations between the PC concentration and the lecithin : sphingomyelin ratio, r = 0.85 ( p < 0.001) and the PC and PG concentrations, r = 0.96 ( p < 0.001) were also found.