The role of centrifugation in the measurement of surfactant in amniotic fluid.

Analysis of amniotic fluid fractions obtained by differential centrifugation has revealed the presence of intact globular-like structures of approximately 1 mu dimensions. These particles, which appear to be representative of fetal lung surfactant, begin precipitating at very low g forces and the extent of their removal by centrifugation was found to significantly alter L/S ratio measurements. This effect is particularly significant when moderate levels of these structures are present, which is usually between 34 and 37 weeks' gestation. False-negative L/S ratios could be attributed to this effect. Centrifugation can be employed to harvest these structures in reasonably pure form and measurement of their concentration, by phospholipid analysis, showed good correlation with fetal lung function in a trial study with 91 patients. These findings suggest that measurement of these surfactant particles harvested from amniotic fluid may provide a simple yet specific index of fetal pulmonary maturity.