Rapid prediction of pulmonary maturity by amniotic fluid lipid globule formation

Utilizing the surface tension (ST) lowering properties of an amniotic fluid lipid extract, it was noted that the amniotic fluid lipid layer formed a subsurface globule when the ST reached 36.9 dynes/cm +/- 0.1877 (SEM). The amount of required extract to achieve globule formation varied with the degree of fetal pulmonary maturity and the volume required could be used to differentiate pulmonary maturity (less than or equal to 320 microliter), transitional status (340 to 440 microliter), and pulmonary immaturity (greater than 460 microliter), as related to fetal outcome (amniotic fluid obtained within 48 hours of delivery). Of the 70 patients studied, the 7 (100%) who developed respiratory distress syndrome (RDS) were predicted correctly. Nine of 70 (12.1%) gave false negative results (predicted pulmonary immaturity, no RDS developed); there were no false positives. Globule measurements of a separate series of 74 samples were compared with their L/S ratios. Twenty-two of 24 (91.7%) samples termed mature had an L/S greater than 2.0, while 32 of 42 with a value termed immature had an L/S less than or equal to 1.9. The physical events in the establishment of the monolayer and subsequent globule formation are discussed. This method now provides a rapid and reliable screening indicator of fetal pulmonary maturity.