Neonatal respiratory morbidity at term and the risk of childhood asthma

Objective: To determine whether neonatal respiratory morbidity at term is associated with an increased risk of later asthma and whether this may explain previously described associations between caesarean delivery and asthma. Design: Retrospective cohort study using Scottish Morbidity Record (SMR) data of maternity (SMR02), neonatal (SMR11), and acute hospital (SMR01) discharges. Setting: Scotland. Participants: All singleton births at term between 1992 - 1995 in 23 Scottish maternity hospitals. Main outcome measures: Hospital admission with a diagnosis of asthma in the principal position between 1992 and 2000. Results: Children who had a diagnosis of transient tachypnoea of the newborn or respiratory distress syndrome were at increased risk of being admitted to hospital with a diagnosis of asthma ( hazard ratio (HR) 1.7, 95% confidence interval ( 95% CI) 1.4 to 2.2, p< 0.001). This association was observed both among children delivered vaginally ( HR 1.5, 95% CI 1.1 to 2.0, p = 0.007) and among those delivered by caesarean section ( HR 2.2, 95% CI 1.6 to 3.0, p< 0.001). In the absence of neonatal respiratory morbidity, delivery by caesarean section was weakly associated with the risk of asthma in childhood ( HR 1.1, 95% CI 1.0 to 1.2, p = 0.004). The strengths of the associations were similar whether the caesarean delivery was planned or emergency and were not significantly altered by adjustment for maternal, obstetric, and other neonatal characteristics. Conclusions: Neonatal respiratory morbidity at term is associated with an increased risk of asthma in childhood which may explain previously described associations between caesarean delivery and later asthma.