Amniotic fluid lecithin: sphingomyelin ratio and fetal lung development.

The normal range and trends of the ratio between lecithin and sphingomyelin in the amniotic fluid, estimated on thin-layer chromatograms, have been established for the last trimester. The accuracy of the ratio as an index of fetal lung development and of the risk of neonatal respiratory distress has been confirmed. The usual increase in the ratio towards term was not found in some pregnancies complicated by diabetes or severe rhesus incompatibility. Determination of the ratio may prove a valuable guide in the management of pregnancies with these complications.