Respiratory distress syndrome and birth order in premature twins.

OBJECTIVE To determine the effect of birth order on respiratory distress syndrome (RDS) in the outcome of twins in a large premature population managed in a modern neonatal intensive care unit. METHODS An historical cohort study design was used to analyse the neonatal outcomes of 301 premature liveborn twin sibling pairs of between 23 and 31 weeks gestation from the Australia and New Zealand Neonatal Network 1995 database. RESULTS Among the 56 twin sibling pairs who were discordant for RDS, the second twin was affected in 41 cases (odds ratio (OR) 2.7, 95% confidence interval (CI) 1.5 to 5.3). The excess risk of RDS in the second twin increased with gestation and was statistically significant for twins above 29 weeks gestation (OR 4.4, 95% CI 1.6 to 15). CONCLUSIONS There is a significant increased risk of RDS associated with being the second born of premature twins, which appears to depend on gestation.