SummaryThe 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.

Summary The lecithin : sphingomyelin area ratio (LSAR) was measured in 108 samples of amniotic fluid obtained after 32 weeks' gestation from 66 pregnant diabetics and in 34 samples from 27 women with latent diabetes during pregnancy. A previously reported finding that the normal terminal rise in the ratio did not occur in approximately one‐third of such patients was confirmed. The clinical value of this test, in timing delivery to minimize the risk of neonatal respiratory distress, is discussed; its routine use in pregnancies complicated by established or latent diabetes is advocated.

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