Heterogeneity of respiratory distress syndrome: Risk factors and morbidity associated with early and late gestation disease

Background: Although respiratory distress syndrome (RDS) is considered a disease of prematurity, there is evidence to suggest heterogeneity between early and late gestation RDS. We examined the epidemiologic features of RDS occurring at early and late gestation. Methods: We conducted a retrospective cohort study including live births in the United States in 2005-06, with information obtained from the National Center for Health Statistics. Early (<32 weeks) and late gestation RDS (≥39 weeks) were contrasted in terms of risk factors and associations with pregnancy complications, obstetric intervention and co-morbidity. Logistic regression was used to quantify the effects of risk factors, while other associations were quantified descriptively. Results: There were 27,971 RDS cases, yielding an incidence of 6.4 per 1000 live births. Early and late gestation RDS differed in terms of risk factors, with factors such as multi-fetal gestation more strongly associated with early (adjusted odds ratio [aOR] 11.6, 95 % confidence interval 11.0-12.2) compared with late gestation RDS (aOR 3.66, 95 % confidence interval 2.68-4.98). The morbidity correlates of early and late gestation RDS also differed substantially; neonatal seizures were less strongly associated with early (OR 5.90, 95 % confidence interval 3.67-9.47) compared with late gestation RDS (OR 33.1, 95 % confidence interval 27.2-40.2), while meconium aspiration syndrome was not significantly associated with early gestation RDS (OR 1.87, 95 % confidence interval 0.94-3.72) and very strongly associated with late gestation RDS (OR 39.8, 95 % confidence interval 34.7-45.6). Conclusions: Differences in risk factors and morbidity correlates of early and late gestation RDS suggest that these entities represent two distinct diseases.