phosphatidylglycerol

Surfactant, produced by type II pneumocytes, is ~75% phosphatidylcholine (especially dipalmitoylphosphatidylcholine), with phosphatidylglycerol (PG) appearing later in gestation (typically after ~35 weeks). Amniotic fluid PG is therefore a marker of fetal lung maturity; presence of PG strongly predicts absence of neonatal respiratory distress syndrome, even in diabetic pregnancies where the L:S ratio can be falsely reassuring. PG also helps stabilize the surfactant monolayer at the air-liquid interface, lowering alveolar surface tension and preventing atelectasis. It is one of the components of exogenous surfactant preparations used to treat preterm RDS.