A modified lecithin/sphingomyelin ratio test for fetal maturity.

Several desirable techniques (rapid chromatogram development, planimetry, acetone precipitation of lecithin, and copper molybdate staining) used in other published lecithin/sphingomyelin (L/S) ratio procedures were integrated into a single L/S ratio test. The resulting test requires only 2 ml of amniotic fluid, can be performed within 75 minutes, and is semiquantitative. Methodology tests showed a high degree of reproducibility without the need for a densitometer: Coefficients of variation for the standards and amniotic fluid samples were 11% and 4%, respectively. Also, a linear relationship was observed between the L/S weight ratios in synthetic mixtures and the corresponding area ratios up to the mature value of 2.5. Clinical evaluation on a normal and high-risk patient population showed excellent reliability: The accuracy in predicting fetal lung maturity and immaturity was 100% and 85%, respectively. Moreover, the numerical value of the L/S ratio in the immature range was found to be indicative of the severity of respiratory distress syndrome. Finally, the relationship between the L/S ratio and gestational age in a normal population was described mathematically by an approximating curve. We concluded from our methodologic and clinical data that the L/S ratio may be determined simply and reliably by means of the procedure described in this report.