PURPOSE OF THE STUDY.
To investigate if cesarean delivery (CD) increases the risk of asthma in childhood and adolescence.
The study population consisted of a cohort of 87 555 Swedish siblings (175 110 children).
This register-based cohort study linked the study population to the Swedish Prescribed Drug Register and the National Patient Data Register. These databases contain prescriptions and inpatient and outpatient visit diagnoses for the majority of the study period. Asthma outcome variables, including medication and asthma diagnosis, were collected at the 10th or 13th year of life (age 10 for children born June 1996 through June 1999 or age 13 for children born June 1993 through May 1996). Diagnostic criteria included a prescription for any asthma medication except for oral β2-agonists dispensed at least twice during the year of follow-up or diagnosis of asthma in the National Patient Data Register. CD was defined as elective if performed before the onset of labor and as emergency after the onset of labor. Data were adjusted for maternal and child characteristics to include child gender, birth weight, gestational age, birth order, hypoxia/asphyxia at birth, Apgar score, maternal age, parental cohabitation, maternal birth country, and maternal BMI.
Of the 87 555 sibling pairs studied, 20 493 had discordant modes of delivery in which 1 sibling was delivered vaginally (VD) and 1 by CD, 1005 were discordant for use of any asthma medication, and 240 were discordant for asthma diagnosis. In cohort analyses, there was an increased risk of asthma in children born via CD compared with those born via VD. When stratified into emergency versus elective CD, emergency CD was associated with a slight increased risk of asthma medication prescription. Sibling control analyses revealed a nonsignificant association between CD and diagnosis of asthma.
There is an increased risk of asthma in children born by emergency but not elective CD when compared with VD. This difference is not well explained by discrepant exposure to vaginal microflora.
The current study is novel as the first sibling control analysis on mode of delivery and asthma. The hygiene hypothesis postulates that the incidence of asthma is increasing in developed regions secondary to decreased exposure to infections, parasites, and noninfectious microorganisms. Without stimulation of infectious disease, the immune system switches from an infection-fighting (Th1) profile to an allergy/asthma-producing (Th2) profile. It has been postulated that children born by CD do not come in contact with vaginal microflora and therefore are more likely to develop a Th2 profile, predisposing them to asthma and other allergic diseases. Based on results of the current study, it is unlikely that exposure to vaginal microflora causes reduced risk of asthma. Results of the current study suggest that maternal/fetal characteristics or indications for CD play a role in subsequent childhood asthma risk.
- Copyright © 2013 by the American Academy of Pediatrics