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.