Phosphatidylinositol and phosphatidylglycerol in amniotic fluid: indices of lung maturity.

The minor phospholipids in amniotic fluid from normal pregnancies were correlated with the well-established index of lung maturity, the lecithin/sphingomyelin (L/S) ratio. When the L/S ratio was less than 1.0, the acidic phospholippids phosphatidylglycerol (PG) and phosphatidylinositol (PI) were absent or low in concentration (0.0 to 2.5 per cent of lipid phosphorus). Parallel to the increase in the L/S ratio to 2.0, the content of PI increased 6.0 to 8.5 per cent of lipid phosphorus. PG, the unique phospholipid of lung surfactant, first appeared and PI concomitantly decreased when the L/S ratio exceeded 2.0, indicating the secretion of mature lung surfactant. Analysis of PI and PG in amniotic fluid as markers of surfactant seems to be of value as an additional index of prenatal evaluation of lung maturity and may be particularly useful when the specimen is contaminated with blood.