The effect of premature rupture of the membranes on the surface activity of amniotic fluid and on the pulmonary function of the newborn.

In 30 patients with rupture of the membranes at 29 to 37 weeks gestation amniotic fluid was collected immediately and within 72 h. The concentration of lung surfactant was estimated by surface tension measurements in the Wilhelmy-balance. In 19 cases the results of the first surface tension measurement predicted lung immaturity, in 17 of these surfactant concentration increased, the last surface tension measurement being consistent with complete pulmonary maturation. None of these infants developed RDS. However, the two newborn infants, in whom serial surface tension measurements had shown no increase of surfactant concentration developed symptoms of RDS. In 11 patients with apparently mature surfactant values immediately after membrane rupture, further amniotic fluid surface tension measurements showed an increase in the concentration of surface active material. The respiratory compliance was measured in 11 healthy neonates and in the two newborn with RDS. The results reflected those of surfactant concentration obtained in amniotic fluid. Premature rupture of the membranes would seem to constitute a stimulus for fetal lung maturation.