Threatened preterm labor: the influence of time factors on the incidence of respiratory distress syndrome.

The interval between the first symptoms of threatened preterm labor and delivery was studied and found to be correlated with the incidence of respiratory distress syndrome (RDS), independent of treatment with corticosteroids or betamimetics and the state of the membranes. The incidence and severity of RDS decreased when labor was postponed for a period ranging from 12 hours to three weeks after admission. The decrease was most marked in a steroid-treated group but also occurred in the placebo-treated and untreated groups. The combination of orciprenaline and betamethasone was more effective in postponing delivery in early pregnancies than was the combination of orciprenaline and placebo. Treatment with betamimetics and corticosteroids is therefore indicated in cases of active preterm labor.