Comparison of amniotic fluid optical density, L/S ratio and creatinine concentration in predicting fetal pulmonary maturity.

The optical density of amniotic fluid at 650 nm (OD650) has been proposed as a rapid means of assessing fetal pulmonary maturity. Two hundred eighty-two amniotic fluid samples were analyzed for OD650, L/S ratio and creatinine concentration, and those values were related to the infants' pulmonary outcome. Among those infants delivered within 72 hours of amniocentesis, pulmonary maturity was predicted accurately in 98.3% by the OD650, 97.7% by the L/S ratio and 97.6% by the creatinine concentration. All three tests were unreliable in predicting pulmonary complications when the tests revealed pulmonary immaturity. OD650 values were found to vary inversely with centrifugation speed, reaffirming the need for standardized processing techniques to achieve reliable results. Marked discrepancies occurred between the diagnoses given by three neonatologists asked to retrospectively evaluate the likely etiology of pulmonary problems in nine infants suspected of having respiratory distress syndrome.