Total surface-active phospholipid/sphingomyelin ratio as an index of fetal lung maturity.

As an index of fetal lung maturity, the ratio of total surface-active phospholipid (phosphatidylethanolamine + phosphatidylinositol + phosphatidyglycerol + lecithin) to sphingomyelin performs as well as or better than any other indicator that we tested, showing 92% sensitivity and 98% specificity. The sensitivity and specificity, respectively, of the other methods were: (a) lecithin/sphingomyelin ratio, 92% and 95%; (b) alkaline phosphatase/glutamyltransferase ratio, 100% and 49%; (c) microviscosity, 75% and 97%; and (d) adsorbance at 650 nm, 50% and 73%. The procedure requires 2 h or less and its simplicity allows it to be offered on a 24 h/day basis without necessitating special training.