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Preterm or early term birth and long-term risk of asthma into midadulthood: a national cohort and cosibling study
  1. Casey Crump1,
  2. Jan Sundquist2,
  3. Kristina Sundquist2
  1. 1Departments of Family Medicine and Community Health and of Population Health Science and Policy, Icahn School of Medicine at Mount Sinai, New York, New York, USA
  2. 2Center for Primary Health Care Research, Lund University, Malmö, Sweden
  1. Correspondence to Dr Casey Crump, Icahn School of Medicine at Mount Sinai, New York, New York, USA; casey.crump{at}


Background Preterm birth is associated with pulmonary complications early in life; however, long-term risks of asthma into adulthood are unclear.

Objective To determine asthma risks from childhood into adulthood associated with gestational age at birth in a large population-based cohort.

Methods A national cohort study was conducted of all 4 079 878 singletons born in Sweden during 1973–2013, followed up for asthma identified from primary care, specialty outpatient and inpatient diagnoses in nationwide registries through 2018 (up to 46 years). Cox regression was used to adjust for potential confounders, and cosibling analyses assessed the influence of unmeasured shared familial (genetic and/or environmental) factors.

Results In 91.9 million person-years of follow-up, 607 760 (14.9%) persons were diagnosed with asthma. Preterm birth was associated with increased risk of asthma at ages <10 years (adjusted HR 1.73; 95% CI 1.70 to 1.75), 10–17 years (1.29; 1.27 to 1.32) and 18–46 years (1.19; 1.17 to 1.22). Across all ages, adjusted HRs further stratified were 3.01 (95% CI 2.88 to 3.15) for extremely preterm (22–27 weeks), 1.76 (1.72 to 1.79) for very or moderately preterm (28–33 weeks), 1.31 (1.29 to 1.32) for late preterm (34–36 weeks) and 1.13 (1.12 to 1.14) for early term (37–38 weeks), compared with full-term (39–41 weeks) birth. These findings were not explained by shared familial factors. Asthma risks were elevated after spontaneous or medically indicated preterm birth and with or without perinatal respiratory complications.

Conclusions In this large national cohort, preterm and early term birth were associated with increased risks of asthma from childhood into midadulthood. Persons born prematurely need long-term follow-up into adulthood for timely detection and treatment of asthma.

  • asthma
  • paediatric asthma

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  • Contributors JS serves as guarantor and affirms that the manuscript is an honest, accurate and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained. All authors had full access to all of the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: all authors. Acquisition of data: JS and KS. Analysis and interpretation of data: all authors. Drafting of the manuscript: CC. Critical revision of the manuscript for important intellectual content: all authors. Statistical analysis: CC and JS. Obtained funding: all authors.

  • Funding This work was supported by the National Heart, Lung, and Blood Institute at the National Institutes of Health (R01 HL139536); the Swedish Research Council; the Swedish Heart-Lung Foundation; and ALF project grant, Region Skåne/Lund University, Sweden.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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