Correlation of amniotic fluid optical density at 650 nm and lecithin/sphingomyelin ratios with phosphatidylglycerol.

In this study we have attempted to correlate amniotic fluid optical density measurements and lecithin/sphingomyelin (L/S) ratios with the presence of phosphatidylglycerol. An 85% correlation (126 of 148) of all three parameters was noted. When the assumption was made that phosphatidylglycerol is indicative of fetal pulmonary maturity, 93 of 94 fluid samples having an optical density at 650 nm greater than or equal to 0.15 had demonstrable phosphatidylglycerol for a 1% false positive rate. In 53 fluid samples having an optical density at 650 nm less than 0.15, phosphatidylglycerol was present in 11 and absent in 42, a 21% false negative rate. The same analyses with lecithin/sphingomyelin ratios showed a 5% false positive rate and a 31% false negative rate.