Objective-To determine the effect of birth order on respiratory distress sy
ndrome (RDS) in the outcome of twins in a large premature population manage
d 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 da
tabase.
Results-Among the 56 twin sibling pairs who were discordant for RDS, the se
cond twin was affected in 41 cases (odds ratio (OR) 2.7, 95% confidence int
erval (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 be
ing the second born of premature twins, which appears to depend on gestatio
n.