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Season of the first trimester of pregnancy predicts sensitisation to food allergens in childhood: a population-based cohort study from Finland
  1. Kaisa Pyrhönen1,2,3,
  2. Esa Läärä4,
  3. Liisa Hiltunen2,3,5,
  4. Minna Kaila6,
  5. Timo Hugg3,
  6. Simo Näyhä3,7
  1. 1South Karelia District of Social and Health Services, Lappeenranta, Finland
  2. 2Unit of General Practice, Oulu University Hospital, Finland
  3. 3Institute of Health Sciences, University of Oulu, Finland
  4. 4Department of Mathematical Sciences, University of Oulu, Finland
  5. 5Health Centre of Oulu, Oulu, Finland
  6. 6Paediatric Research Centre, Tampere University Hospital and University of Tampere, Finland
  7. 7Finnish Institute of Occupational Health, Oulu, Finland
  1. Correspondence to Dr Kaisa Pyrhönen, South Karelian Institute, Lappeenranta University of Technology, PO Box 20, FIN-53851 Lappeenranta, Finland; kaisa.pyrhonen{at}


Objective To examine whether the season of birth or season of the early phase of gestation is associated with sensitisation to food allergens in children, with special reference to mothers' pollen exposure in spring.

Design A population-based cohort study linking information from a questionnaire survey to allergy tests performed on the target population and regional pollen counts.

Population Children born in 2001–6 who were resident in the province of South Karelia, Finland, at the time of the survey (N=5920).

Main Outcome Measures A positive result in any food allergy test or food-specific immunoglobulin E test (sIgE).

Results The cumulative incidence of a positive food allergy test up to the age of 4 years was highest among children born in October–November (10%) and lowest among those born in June–July (5%), and correspondingly highest among children who were in their 11th gestational week in April–May (11%), the season of high concentrations of birch and alder pollen, and lowest among those reaching that stage in December–January (6%). The amplitude of seasonal variation in any test, estimated as the relative ratio between the peak and trough of the smoothed incidence curve over the year, was 2.03 (95% CI 1.52 to 2.76). The amplitudes of positive sIgE were especially pronounced for milk (3.07; 95% CI 1.81 to 5.50) and egg (3.03; 95% CI 1.86 to 5.18).

Conclusions Children having their early gestational period in the pollen season for broad-leafed trees are more prone to sensitisation to food allergens than other children.

  • Allergy
  • children
  • epidemiology fq
  • population survey
  • seasonal variation

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  • Funding The project and the work of the principal investigator were mainly funded by the Social Insurance Institution of Finland and partly by EVO grants from the hospital districts of South Karelia, Northern Ostrobothnia and Pirkanmaa. The work of the second author was supported by a research grant for senior scientists (no 120146) from the Academy of Finland. The City of Lappeenranta funded the mailing of the questionnaires, and other costs were covered by personal grants to the principal investigator from the Finnish Cultural Foundation (Lahja and Lauri Hotinen Fund), the Viipuri Tuberculosis Foundation, the Tyyni Tani Foundation, Kymenlaakson Terveyden Turva ry, the Allergy Foundation and the Medical Society Duodecim in South Karelia.

  • Competing interests None declared.

  • Ethics approval This study was conducted with the approval of the the Ethical Committee of the Northern Ostrobothnia Hospital District.

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