Asthma diagnosis and treatment
Mode of delivery at birth and development of asthma: A population-based cohort study

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Background

To test the hygiene hypothesis, previous studies have assessed the relationship between mode of delivery at birth and asthma incidence, but the results have been inconsistent because of potential selection and ascertainment biases.

Objective

To assess the relationship between mode of delivery at birth and asthma by following all children born in Rochester, Minn, between 1976 and 1982.

Methods

From the birth certificate, we determined mode of delivery (cesarean section vs vaginal delivery). Asthma status during the first 7 years of life was ascertained from comprehensive medical record reviews. The association between mode of delivery and asthma status was evaluated in a proportional hazards model adjusted for sex, birth weight, maternal education, and maternal age.

Results

The cumulative incidence rates of asthma among children who were born by cesarean section and vaginal delivery were 3.2% versus 2.6%, 4.6% versus 4.6%, 4.6% versus 5.8%, and 5.7% versus 6.7% at the 1st, 3rd, 5th, and 7th years of life, respectively. The adjusted hazard ratios for cesarean section in predicting asthma and wheezing episode were 0.93 (95% CI, 0.6-1.4; P = .71) and 0.93 (95% CI, 0.7-1.3; P = .67), respectively.

Conclusion

Mode of delivery is not associated with subsequent risk of developing childhood asthma or wheezing episodes. Because the effect of mode of delivery on a risk of developing asthma or wheezing episodes varies over time (ie, age), selection of the study subjects according to their ages may have influenced the findings of previous studies with a shorter follow-up period.

Section snippets

Study design and setting

The study was a retrospective, population-based cohort study.

Rochester, Minn, is centrally located in Olmsted County, and greater than 60% of the county population resides within the city limits. In 1980, the population of Rochester was 57,890 (97% white). With the exception of a higher proportion of the working population employed in the health care industry, characteristics of the City of Rochester and Olmsted County populations were similar to those of the US white population.36, 37, 38

Incidence cohort

During the period 1976 to 1982, 7463 children were born to mothers who were residents of the City of Rochester at the time of their delivery. Of these children, 21 children died, 324 children were born after prolonged rupture of membranes, and 12 were born after the vaginal procedure was converted to a cesarean section, yielding 7106 children in the birth cohort who met the study criteria. Of the remaining 7106 children, a total of 342 met the criteria for either definite or probable asthma

Discussion

Our study results show that mode of delivery at birth was not associated with risk of subsequent development of childhood asthma or wheezing episodes in the 1976 to 1982 Rochester birth cohort during their first 7 years of life. However, as depicted in Table III, the relationship between childhood asthma or wheezing episodes and mode of delivery at birth is not constant but varies over time.

According to our study results, during the first 2 years of life or so, children born by cesarean section

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    Supported by the Scholarly Clinician Award of the Mayo Foundation.

    Disclosure of potential conflict of interest: All authors—none disclosed.

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