The epidemiology of respiratory distress syndrome in Norway.

Information collected through the Medical Birth Registry of Norway on a seven-year cohort of 457,465 live births for the years 1967--73 were used to determine the factors associated with the risk of respiratory distress syndrome (RDS). A total of 1235 cases were identified and 510 of these died, resulting in an incidence rate of 2.7 and a mortality rate of 1.1 per 1000 live births. From a geographic breakdown of counties there was no association of the incidence or mortality of RDS with such environmental factors as latitude, longitude, urbanization, industrialization or level of obstetric care. There was an increase in reported incidence and mortality over time, and a slight peak during fall months. The major factors associated with the risk of RDS in Norway were birth weight, gestational age, male sex, cesarean sections and some other complications of pregnancy or delivery. When rates were adjusted for birth weight and gestational age there was no association with maternal age, parity or marital status. Such adjustments reversed the risk of RDS among multiple births to a rate lower than that for single births.