Sonographically detected free-floating particles in amniotic fluid predict a mature lecithin-sphingomyelin ratio

Amniocentesis for the determination of fetal lung maturity is associated with some morbidity, and so the prediction of a mature fetus by noninvasive means could be useful in managing certain high-risk patients. In the first portion of this study, 467 amniotic fluid specimens were classified into one of five groups based on the turbidity and particulate matter present. The mean lecithin: sphingomyelin (L/S) ratios and the proportion of mature L/S values increased with increasing turbidity of the amniotic fluid. In the second portion of this study, the presence of amniotic fluid free-floating particles (FFPs) detected by real-time ultrasound was correlated with fetal lung maturity. When FFPs were present, the L/S was uniformly mature, but when FFPs were absent, the L/S was mature in 74% of patients (P less than 0.01). Among the patients in whom the L/S ratios were mature, 39/110 were associated with positive FFPs (sensitivity = 35%). This preliminary study suggests that the presence of FFPs on real-time ultrasound could be used to confirm fetal lung maturity.