The quantitative and qualitative analyses of lecithin in the human amniotic fluid in relation to the antenatal prediction of developing respiratory distress syndrome were described. Surfactant lecithin (disaturated and/or dipalmitoyl lecithin) was estimated for the first time in 42 amniotic fluid specimens of 21–42 weeks gestation. Surfactant lecithin was present in considerable amounts in specimens obtained near or at term except in the ones associated with infants who subsequently developed respiratory distress syndrome. One infant developed typical respiratory distress syndrome despite the normal total lecithin concentration of amniotic fluid at birth. The fatty acid analysis, however, revealed that the surfactant lecithin concentration was extremely low, showing a great discrepancy between total lecithin and surfactant lecithin concentrations. Thus the estimation of disaturated and/or dipalmitoyl lecithin in the amniotic fluid seems to be the most precise sign of a potential risk of respiratory distress syndrome.

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