Fetal lung maturity. I. Mode of onset of premature labor. Influence of premature rupture of the membranes.

In a prospective study of 133 spontaneous premature deliveries the relation between premature rupture of the membranes (PRM) and development of respiratory distress syndrome (RDS) in newborn infants is examined. PRM is associated with a significantly decreased incidence of RDS in newborn infants (P less than 0.002). This relation is valid at a gestational age of 28 weeks or more and a birthweight greater than 1000 g. Total respiratory morbidity in newborn infants (transient tachypnea + RDS) is also significantly decreased when labor is associated with PRM (P less than 0.005). Assessment of the influences of sex of the infant, fetal asphyxia, and delivery by cesarian section shows that PRM bears a stronger relation than each of these individual factors to a decreased incidence of RDS. Duration of the latent period has no influence on protection from RDS, and it is suggested that fetal lung maturity occurs before the membranes rupture.