Original Article
Risk of Asthma in Late Preterm Infants: A Propensity Score Approach

https://doi.org/10.1016/j.jaip.2015.03.018Get rights and content

Background

The risk of asthma, specifically in former late preterm infants, has not been well defined. Covariate imbalance and lack of controlling for this has led to inconsistent results in prior studies.

Objective

The objective of this study was to determine the risk of asthma in former late preterm infants using a propensity score approach.

Methods

The study was a population-based birth cohort study. Study subjects were all children born in Rochester, Minn, between 1976 and 1982. Asthma status during the first 7 years of life was assessed by applying predetermined criteria. The propensity score was formulated using 15 covariates by fitting a logistic regression model for late preterm birth versus term birth. We applied the propensity score method to match late preterm infants (34 0/7 to 36 6/7 weeks of gestation) to term infants (37 0/7 to 40 6/7 weeks of gestation) within a caliper of 0.2 standard deviation of logit of propensity score.

Results

Of the eligible 7040 infants, 5915 children had complete data. Before propensity score matching, late preterm infants had a higher risk of asthma (20 of 262, 7.6%) compared with full-term infants (272 of 5653, 4.8%) (P = .039). There was significant covariate imbalance between comparison groups. After matching with propensity scores, we found that former late preterm infants had a similar risk of asthma to the matched full-term infants (6.6% vs 7.7%, respectively, P = .61), and the result was consistent with covariate-adjustment Cox regression models controlling for significant covariates (P = .57).

Conclusion

A late preterm birth history is not independently associated with childhood asthma, as the reported risk of asthma among former late preterm infants appears to be due to covariate imbalance.

Section snippets

Methods

This study protocol was approved by Institutional Review Boards at Mayo Clinic and Olmsted Medical Center.

Characteristics of subjects

During the period 1976 to 1982, a total of 7463 children were born to mothers who were residents of the city of Rochester at the time of their delivery. Twenty-one children died at birth, yielding 7442 children in the birth cohort for follow-up. An additional 402 infants born less than 34 weeks of gestation were excluded. This left 7040 children in our study (median follow-up of 3.8 person-years). Of these 7040 children who met the study eligibility, 333 were born LPT (4%) (6707 children were

Discussion

In our population-based birth cohort study using the PSA to reduce covariate imbalance, we found that there was no significant difference in risk of asthma between LPT and term infants. The PSA might be a useful tool for research concerning asthma epidemiology where random assignment of exposure is not feasible.

We believe that the finding of no association between LPT and risk of asthma in our study is not due to lack of statistical power. For example, the literature showed that the effect size

Acknowledgments

We thank the Pediatric Asthma Epidemiology Research Unit's staff for their comments and suggestions. Research reported in this publication was supported by the National Institute of Allergy and Infectious Diseases (R21 AI101277) and the Scholarly Clinician Award from the Mayo Foundation. It was also made possible by the support from the National Institute on Aging of the National Institutes of Health under Award Number R01AG034676.

References (40)

  • I. Broder et al.

    Epidemiology of asthma and allergic rhinitis in a total community, Tecumseh, Michigan: IV. Natural history

    J Allergy Clin Immunol

    (1974)
  • S. Katusic et al.

    Potential influence of migration bias in birth cohort studies

    Mayo Clin Proc

    (1998)
  • K. Yoo et al.

    The impact of electronic medical records on timeliness of diagnosis of asthma

    J Allergy Clin Immunol

    (2007)
  • Vital signs: asthma prevalence, disease characteristics, and self-management education: United States, 2001-2009

    MMWR Morb Mortal Wkly Rep

    (2011)
  • C. Anandan et al.

    Is the prevalence of asthma declining? Systematic review of epidemiological studies

    Allergy

    (2010)
  • The Center for Disease Control and Prevention. National Center for Health Statistics. Are preterm births on the decline...
  • C.D. Mallen et al.

    Birth-related exposures and asthma and allergy in adulthood: a population-based cross-sectional study of young adults in North Staffordshire

    J Asthma

    (2008)
  • B.A. Raby et al.

    Low-normal gestational age as a predictor of asthma at 6 years of age

    Pediatrics

    (2004)
  • N.K. Goyal et al.

    Adherence to discharge guidelines for late-preterm newborns

    Pediatrics

    (2011)
  • G.J. Escobar et al.

    Recurrent wheezing in the third year of life among children born at 32 weeks' gestation or later: relationship to laboratory-confirmed, medically attended infection with respiratory syncytial virus during the first year of life

    Arch Pediatr Adolesc Med

    (2010)
  • Cited by (0)

    This work was supported by the Clinician Scholarly Award from the Mayo Foundation and it was made possible by the Rochester Epidemiology Project (R01-AG34676) from the National Institute on Aging.

    Conflicts of interest: The authors declare that they have no relevant conflicts.

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