Correlation of absorbance at 650 nm with the presence of phosphatidylglycerol in amniotic fluid.

Amniotic fluid absorbance at 650 nm was correlated with the presence of phosphatidylglycerol (PG) in the isolated surfactant fraction (10,000-g pellet). Shake test results were included. Two hundred ninety-seven samples were analyzed. PG was present in 222 of 226 samples in which the absorbance was greater than or equal to 0.250 and absent from 48 of 71 with an absorbance less than 0.250. PG was present in all 166 samples with a positive shake test and absent in 52 of 131 samples with a negative one. In 65 samples in which the shake test was negative and the absorbance greater than or equal to 0.250, PG was present in all but 4. The false-positive rate for the prediction of respiratory distress syndrome was 0.8% for the Shake test and 0.6% for the absorbance measurement. The results support the usefulness of the absorbance measurement as a simple and reliable procedure for assessing fetal lung maturity.