Meconium has no lecithin or sphingomyelin but affects the lecithin/sphingomyelin ratio

OBJECTIVE: Although a few studies have evaluated the effect of meconium on the lecithin/sphingomyelin ratio for testing of fetal lung maturity, to dat e these studies have assessed only the lecithin-sphingomyelin ratio of amni otic fluid contaminated with meconium. The purpose of this study was (1) to determine whether meconium by itself has a lecithin/sphingomyelin ratio an d, if so, (2) to determine whether the lecithin/sphingomyelin ratio is cons tant. STUDY DESIGN: A lecithin/sphingomyelin ratio was obtained by standard thin- layer chromatography on the first meconium steal of 20 neonates between 31 weeks and term. A quantitative assay was then performed on a sample from ea ch gestational age (7 samples ranging from 31 weeks to term) to confirm the presence of lecithin and sphingomyelin. RESULTS: The 20 samples had atypical thin-layer chromatographic migratory p atterns in the zones for lecithin and sphingomyelin. The presumed lecithin/ sphingomyelin ratios ranged from 1.1 to 3.6, with no correlation with gesta tional age. However, the quantitative assay did not detect the presence of lecithin or sphingomyelin in any of the analyzed samples. CONCLUSIONS: Meconium does not appear to contain lecithin or sphingomyelin but has an unidentified moiety whose migratory pattern, as shown by qualita tive standard thin-layer chromatography, is similar to that of lecithin wit h sphingomyelin. Therefore the presence of meconium in amniotic fluid may f alsely raise or lower the lecithin/sphingomyelin ratio and confuse fetal lu ng maturity interpretations.