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Caesarean increases asthma risk
One in four births in the UK is by Caesarean
Babies born by Caesarean section are more prone to developing asthma, say Dutch researchers.
In a study of almost 3,000 children, birth by Caesarean was associated with a 80% increased risk of asthma by age eight compared with vaginal birth.
The association was even stronger in children whose parents had allergies, suggesting a genetic predisposition to the disease, it is reported in Thorax.
Previous research has linked Caesareans with the development of allergies.
In total, the team looked at 2,917 children, 247 of whom were born by caesarean.
The mother should be informed of the risk of asthma for her child, especially when the parents have a history of allergy or asthma
Dr Caroline Roduit
Around 12% of the children were diagnosed with asthma for which they were treated with inhaled steroids by the time they were eight years old.
The researchers found that the 9% of children who had two allergic parents were almost three times more likely to be asthmatic by the time they were eight compared with children whose parents were not allergic.
Study leader, Dr Caroline Roduit, now based at the Children's Hospital of Zurich, Switzerland, said rates of asthma had soared in industrialised countries in parallel with a rise in Caesarean section births, which have increased from 5% in the 1970s to more than 30% in 2000.
She suggested that one reason for the association between Caesareans and asthma could be the priming of the immune system after birth.
Other research has shown babies born by Caesarean are not exposed to microbes as soon as babies born by vaginal delivery.
Previous studies in this area have produced conflicting results but the authors said the size of the study, the long monitoring period and and the definition of asthma to include inhaled steroids, strengthened the findings.
"The increased rate of Caesarean section is partly due to maternal demand without medical reason," said Dr Roduit.
"In this situation the mother should be informed of the risk of asthma for her child, especially when the parents have a history of allergy or asthma."
Dr Mike Thomas, chief medical adviser to the charity Asthma UK, said previous studies had also suggested that Caesarean section might increase the risk of asthma.
He said: "Sometimes a Caesarean section is needed for medical reasons, but where possible a natural birth is better."
Thorax. Published Online First: 3 December 2008. doi:10.1136/thx.2008.100875
Copyright © 2008 BMJ Publishing Group Ltd & British Thoracic Society
Asthma at 8 years of age in children born by cesarean section
Caroline Roduit 1, Salome Scholtens 2, Johan C de Jongste 3, Alet H Wijga 1, Jorrit Gerritsen 4, Dirkje S Postma 5, Bert Brunekreef 2, Maarten O Hoekstra 6, Rob Aalberse 7 and Henriette A Smit 1*
1 National Institute for Public Health and the Environment, Bilthoven, Netherlands
2 Institute for Risk Assessment Sciences, Utrecht University, Netherlands
3 Department of Pediatrics, Division of Respiratory Medicine, Erasmus MC – Sophia, Rotterdam, Netherlands
4 Beatrix Children’s Hospital, University Medical Centre Groningen, Netherlands
5 University Medical Centre Groningen, Netherlands
6 Centre for Paediatric Allergology, Wilhelmina Children's Hospital, Netherlands
7 Sanquin Research, Amsterdam, Netherlands
* To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
Accepted 7 September 2008
Background: Cesarean section might be a risk factor for asthma due to a delayed microbial colonization, but the association remains controversial.
Objective: To investigate prospectively whether children born by cesarean section are more at risk of having asthma in childhood, and sensitization at the age of 8 years taking into account the parental allergic status.
Methods: We studied 2,917 children, who participated in a birth cohort study and followed for 8 years. The definition of asthma included wheeze, dyspnea and prescription of inhaled steroids. In a subgroup (n=1,454), serum IgE antibodies for inhalant and food allergens were measured at 8 years.
Results: In the total study population, 12.4% (362) of the children had asthma at the age of 8 years. Cesarean section, with a total prevalence of 8.5%, was associated with an increased risk of asthma (odds ratio [OR], 1.79; 95% confidence interval [CI], 1.27-2.51). This association was stronger among predisposed children (with two allergic parents: OR, 2.91; 95% CI, 1.20-7.05; with only one: OR, 1.86; 95% CI, 1.12-3.09) than in children with non-allergic parents (OR, 1.36; 95% CI, 0.77-2.42). The association between cesarean section and sensitization at the age of 8 years was significant only in children of non-allergic parents (OR, 2.14; 95% CI, 1.16-3.98).
Conclusions: Children born by cesarean section have a higher risk of asthma than those born by vaginal delivery, particularly children of allergic parents. Cesarean section increases the risk for sensitization to common allergens, in children with non-allergic parents only.
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