Fetal pulmonary maturity: Relationship between optical density (650 nm) to the lecithin/sphingomyelin ratio and phosphatidylglycerol in amniotic fluid

An optical density value ?0.15 at A_{650 nm} of amniotic fluid obtained through transabdominal amniocentesis from a high risk obstetrical population, which excluded diabetes mellitus, isoimmunization, and amniotic fluid infection, correlated 98.6% with a mature lecithin to sphingomyelin ratio ($\text{L}\text{S}$) ? 2.0% and 41.6% with the presence of phosphatidylglycerol (PG). The corresponding false positive rates were 1.4% and 16.8%, respectively. In 30 infants delivered within 48 h of testing, A_{650 nm} ?0.15 correlated 100% with absence of respiratory distress syndrome. A_{650 nm} is not recommended for Rhesus immunized gestations, diabetic pregnancies and amniotic fluid infection due to a high false positive rate with A_{650 nm} compared to $\text{L}\text{S}$ and PG.