Assessment of surfactant activity in amniotic fluid for evaluation of fetal lung maturity

A method was developed which consistently detected surfactant activity in amniotic fluid from term pregnancies. Amniotic fluid was mixed with Sephadex and, following low-speed centrifugation, the surface-active material was recovered in the supernatant, free of cells and debris. Fifty-four samples from normal term pregnancies were surface active regardless of contamination with blood or meconium. Samples obtained at delivery of 6 normal premature infants were also surface active. By contrast, amniotic fluid taken at delivery of 6 infants who developed respiratory distress revealed little or no surface activity. The lecithin to sphingomyelin ratio in the latter 6 cases was low as expected. The results indicate that the above simple, rapid method provides consistent and reliable information relating to the state of surfactant function of the developing fetal lung and that this method may effectively screen prior to delivery infants at risk of developing the respiratory distress syndrome.