Letters

Prenatal and perinatal risk factors for psychiatric diseases of early onset

BMJ 1999; 318 doi: https://doi.org/10.1136/bmj.318.7198.1622 (Published 12 June 1999) Cite this as: BMJ 1999;318:1622

Results are different if seasons are categorised differently

  1. Pirkko Räsänen (pirkko.rasanen@oulu.fi), Senior research fellow,
  2. Helinä Hakko, Biostatistician,
  3. Marjo-Riitta Järvelin, Professor
  1. Department of Psychiatry, University of Oulu, FIN-90210 Oulu, Finland
  2. Department of Public Health Science and General Practice, FIN-90220 Oulu
  3. Department of Neuroscience, Psychiatry, Ulleråker, University of Uppsala, S-750 17 Uppsala 17, Sweden

    EDITOR—Hultman et al found that late winter births are associated with increased risks of schizophrenia and affective psychosis, the odds ratios being 1.4 and 1.5 respectively.1 The authors presented the excess of late winter births as one of their key messages, although the finding reached significance only among male subjects with affective psychosis.

    View this table:

    Odds ratios (with 95% confidence intervals) for incidence of schizophrenia and numbers of births in relation to season of birth in northern Finland 1966 birth cohort study

    Using the northern Finland 1966 birth cohort (5636 male and 5381 female subjects), we partially replicated Hultman et al's study. The cohort is a genetically homogeneous population, and data are available on biological, socioeconomic, environmental, and health conditions for every individual from mid-pregnancy of their mother to the age of 31. Psychiatric diagnoses were made on the basis of extracts from the Finnish national hospital discharge register and a detailed diagnostic validation process.2 Birth seasonality was examined separately in those with schizophrenia (Diagnostic and Statistical Manual of Mental Disorders, third edition, revised, code 295; n=105) and those …

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