Abstract
BackgroundCaesarean section (CS) has been reported to increase the risk of asthma in offspring. This may be due to that infants delivered by CS are unexposed to vaginal flora, according to the ‘hygiene hypothesis’.ObjectiveOur aim was to investigate if CS increases risk of childhood asthma, and if the risk increase remains after adjustment for familial confounding using sibling design.MethodsA register-based cohort study with 87 500 Swedish sibling pairs was undertaken. Asthma outcome variables were collected from national health registers as diagnosis or asthma medication (ICD-10 J45-J46; ATC code R03) during the 10th or 13th year of life (year of follow-up). Mode of delivery and confounders were retrieved from the Medical Birth Register. The data were analysed both as a cohort and with sibling control analysis which adjusts for unmeasured familial confounding.ResultsIn the cohort analyses, there was an increased risk of asthma medication and asthma diagnosis during year of follow-up in children born with CS (adjusted ORs, 95% CI 1.13, 1.04–1.24 and 1.10, 1.03–1.18 respectively). When separating between emergency and elective CS the effect on asthma medication remained for emergency CS, but not for elective CS, while both groups had significant effects on asthma diagnosis compared with vaginal delivery. In sibling control analyses, the effect of elective CS on asthma disappeared, while similar but non-significant ORs of medication were obtained for emergency CS.Conclusions and Clinical RelevanceAn increased risk of asthma medication in the group born by emergency CS, but not elective, suggests that there is no causal effect due to vaginal microflora. A more probable explanation should be sought in the indications for emergency CS.
Highlights
The prevalence of childhood asthma and allergic disease increased up to recently in many nations around the world, which implies that a substantial proportion of the risk of having the disease is attributable to environmental factors [1, 2]
In the main sibling population, 9.4% were delivered with Caesarean section (CS), of which 5.4% were emergency and 4.2% elective caesareans
7.0% of the children had any asthma medication (6.8% of those delivered with vaginal delivery (VD), 7.9% if elective CS and 8.2% if born with emergency CS) and 1.6% of the children had an asthma diagnosis (1.5% of those delivered with VD, 2.0% if elective CS and 2.1% if born with emergency CS)
Summary
The prevalence of childhood asthma and allergic disease increased up to recently in many nations around the world, which implies that a substantial proportion of the risk of having the disease is attributable to environmental factors [1, 2]. The rationale why CS could increase the risk of asthma has been referred to a modified intestinal microflora in those unexposed to the vaginal flora, according to the ‘hygiene hypothesis’ [15]. It has been recently shown by Schlintzig et al that. Caesarean section (CS) has been reported to increase the risk of asthma in offspring This may be due to that infants delivered by CS are unexposed to vaginal flora, according to the ‘hygiene hypothesis’. Objective Our aim was to investigate if CS increases risk of childhood asthma, and if the risk increase remains after adjustment for familial confounding using sibling design. The data were analysed both as a cohort and with sibling control analysis which adjusts for unmeasured familial confounding
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