Amniotic fluid phosphatidylinositol and phosphatidylglycerol. I. Normal pregnancies.

Phosphatidylinositol (PI) and phosphatidylglycerol (PG) appear normally in the amniotic fluid during the last weeks of pregnancy. The present study indicated as have previous studies (5, 6, 8, 10) that these phospholipids are linked to the surfactant system in the fetal lung. The concentrations of lecithin (L), PI, PG and sphingomyelin (S) were measured in 207 samples from 165 normal pregnancies. The augmentation in PI was found to parallel that in lecithin, and the PI/S ratios reached maximum values at about 30 weeks of gestation. The augmentation in PG appeared about two weeks later. Eleven premature infants who contracted respiratory distress syndrome (RDS) had significantly lower PG concentrations than 15 premature infants with no RDS (p less than 0.01). No correlation to the PI concentrations could be observed. All but one of the 11 affected infants had low L/S ratios.