Six alternative methods to the lecithin/sphingomyelin ratio in amniotic fluid for assessing fetal lung maturity.

Abstract

During the last trimester of human fetal gestation, lung surfactant is synthesized and secreted into the alveolar space, and becomes detectable in amniotic fluid. Pulmonary surfactant is composed of phospholipids, neutral lipids including cholesterol, and specific apoproteins, and functions to lower surface tension and facilitate gas exchange in the lung. A deficiency of surfactant is associated with respiratory distress syndrome, which can be life-threatening in premature infants. As a test for fetal lung maturity, the most widely accepted method remains the analysis of amniotic fluid for surfactant-derived lecithin expressed as a ratio to sphingomyelin. 1 This tes~ has a high sensitivity and specificity, but employs thin-layer chromatography which is laborious and time-consuming. The potential exists to estimate other components of lung surfactant in amniotic fluid, such as the apoprotein, fatty acid or phospholipid components, or to measure physical properties of surfactant-containing lamellar bodies, such as their number or size. The aim of this study was to examine six methods as more practical alternatives to the lecithin/sphingomyelin (L/S) ratio for the estimation of fetal lung maturity from the analysis of amniotic fluid. In keeping with current trends in clinical laboratory practice, of particular interest were methods that could be automated and/or took less than 1h to produce a result. Forty-four amniotic fluid specimens received by two Adelaide hospitals (Queen Victoria Maternity Hospital and the Flinders Medical Centre) over a I year period were entered into the study. Each of the samples was obtained from an individual patient by transabdominal