Diagnosis of fetal maturity by amniotic fluid phospholipids

The Measurement of the Lecithin-Sphingomyelin Ratio of Amniotic Fluid after Thin-Layer Chromatography

The estimation of the lecithin-sphingomyelin (L.S.) ratio on thin-layer chromatograms has been shown to vary depending upon the stain used to identify the phospholipids and the method employed to estimate the two components. The factors involved in causing these variations have been evaluated using standard phospholipid solutions and confirmed in clinical material. Staining with a phosphomolybdic acid stain followed by transmission densitometry was found to be an accurate and sensitive method for clinical purposes.

Determination of phospholipids in biological samples by an improved densitometric method on thin-layer chromatograms

The quantitative determination of the different phospholipids present in samples of bile, liver or plasma has been performed by densitometric scanning of high-performance thin-layer chromatography plates. These have been developed as follows: pre-treatment with sulphuric acid-ethanol mixture, staining with ethanol-modified molybdenum blue reagent and post-treatments with water and ethanol added with a small quantity of sulphuric acid. The sequential treatment, which introduces some modifications in a previously described procedure, allowed a linear and stable colour response for phosphorous-containing lipids on uniform and colourless background. The calibration of each plate with standard mixture was required for obtaining results in good agreement with other routine methods of determination.

Methods of evaluating fetal lung maturity

Respiratory distress syndrome occurs in infants born with immature lungs. The immature fetal lung lacks an adequate supply of surfactant, a phospholipid-rich substance which is produced in the type II cells of the alveolar epithelium. In the fetus, surfactant is secreted into the potential air spaces of the lung and passes into the amniotic fluid as gestation proceeds. It is now clear that most methods currently in use for assessing fetal lung maturity depend on the detection of a sudden release of surfactant into the amniotic fluid as the lung reaches a critical stage of maturity. These methods, which include the lecithin/sphingomyelin ratio, the lung profile, total phospholipid or lecithin concentration, fluorescence depolarization, lamellar body phospholipid concentration, and the "shake" test, are reviewed in the light of recent understanding of the nature of surfactant. In assessing each method, we have examined possible sources of error in performing the test in the laboratory, factors which could theoretically limit its ability to reflect the state of fetal lung maturity and current information regarding its reliability, in terms of clinical performance. Guidelines for future research in this area are also suggested.

Amniotic fluid lecithin/sphingomyelin ratio in complicated pregnancies

Amniotic fluid (AF) lecithin/sphingomyelin (L/S) rations were obtained in 223 pregnancies. Gestations complicated by maternal diabetes (71), vascular disease (50), and fetal growth retardation (47) were included. Elevated L/S ratios at 34 to 36 weeks' gestation were observed to accompany maternal vascular disease; higher rat;os were also related to fetal sex (female) and race (black). Declining L/S rations were observed in 14 of 35 diabetic patients studied serially (40 per cent) and were accompanied by increased perinatal morbidity and deaths. These data suggest an urgent need for further studies concerning the clinical usefulness of a serial decline in the L/S ration as a predictor of fetal compromise.

A prospective evaluation of the lecithin/sphingomyelin ratio and the rapid surfactant test in relation to fetal pulmonary maturity

Fetal lung maturity was correlated to the results of amniatic fluid analysis in 578 samples obtained over a 2 1/2 year interval. Lecithin/sphingomyelin (L/S) ratios obtained by planimetric and densitometric methods were compared to the rapid surfactant test (RST). Both the planimetric L/S ratio (P L/S) and the densitometric L/S ratio (D L/S) correlated positively in a highly significant fashion with the RST. Both RST and D L/S were reliable in predicting fetal lung maturity (99 to 100 per cent, respectively). The RST was the most reliable test for fetal lung immaturity (69 per cent). Therefore, this series indicates that the RST could be used as a primary method with the D L/S being useful as an additional indicator of fetal maturity when the RST was intermediate, or the sample contaminated with blood and/or meconium.