An investigation of the relationship between cesarean section birth and respiratory distress syndrome of the newborn.

To clarify the nature of the association between respiratory distress syndrome and Cesarean section birth, a study was conducted which compared 273 premature (36 weeks or less) Cesarean-delivered infants with 341 premature vaginally delivered infants who were born at the University of Washington Hospital from January 1, 1977 through March 31, 1980. The gestational age-adjusted probability of respiratory distress syndrome was higher among the Cesarean cohort compared with the vaginal cohort (38.2% vs. 27.6%, odds ratio = 1.63, 95% confidence interval = 1.11-2.39). Three alternative explanations for the association of Cesarean section with respiratory distress syndrome other than causation were tested, and each was rejected. The association was not explained by 1) improper timing of elective Cesarean deliveries; 2) misclassification of cases of mild, transient respiratory distress (which may be more common after Cesarean birth) as respiratory distress syndrome; or 3) the differences in the occurrence of pregnancy complications preceding Cesarean births compared with vaginal births. Lack of labor appears to account for part of the increased risk of respiratory distress syndrome among infants delivered by Cesarean section. The gestational age-adjusted probabilities of respiratory distress syndrome were 47.0% for Cesarean birth without labor, 35.4% for Cesarean birth preceded by labor, and 27.6% for vaginal birth.