Accurate photodensitometric measurement of the lecithin: sphingomyelin ration after elimination of the acidic phospholipids from extracts of amniotic fluid specimens.

Treatment of human amniotic fluid lipids dissolved in a chloroform/methanol (9:1, v/v) mixture by batchwise addition of diethylaminoethyl cellulose in a dry state proved to be an easy and rapid procedure for the removal of the acidic phospholipids which may interfere in the photodensitometric evaluation of the lecithin: spingomyelin ratio on a thin-layer chromatogram. This method was used for the measurement of the lecithin: sphingomyelin ratio in a series of normal and abnormal pregnancies. Ratios higher than expected from gestational age were observed in stressed pregnancies. A significant elevation of the ratio was also observed under treatment by dexamethasone.