Surface tension of amniotic fluid lipid extracts: prediction of pulmonary maturity.

The surface tension (ST)-lowering properties of an amniotic fluid lipid extract can provide a rapid and reliable means of predicting pulmonary maturity. One hundred and eleven samples from 91 patients were analyzed. A surface tension of less than 56 dynes per centimeter at 120 microliter of extract and less than 46 dynes per centimeter at 220 microliter of extract denoted pulmonary maturity. Values greater than these indicated immaturity. Among fluid samples studied within 48 hours of delivery for the presence or absence of respiratory distress syndrome (RDS) in 71 patients, there were no false positive ST values, while 7 of 22 patients with immature values developed RDS. Surface tension correlates well with the lecithin/sphingomyelin (L/S) ratio but provides clearer definition than the L/S ratio when compared to outcome. Blood and meconium contamination make the surface tension of fluid from babies with pulmonary immaturity appear mature. Identical twins with dissimilar ST values and outcome, as well as serial samples from individual patients, are analyzed and discussed.