Obstetric factors, urbanization and psychosis

Background. Epidemiologic evidence as early as the 1930s has suggested urba nization is linked to schizophrenia, either by place of admission, place of upbringing, or, more recently, place of birth. In the past decade, obstetr ic complications have been implicated in the etiology of schizophrenia. Methods. With appropriate protections for anonymity, the files of the Danis h Medical Birth Register were linked with the files of the Danish Psychiatr ic Case Register. The linkage produced 132 cases of schizophrenia and 69 ca ses of affective psychosis, who were born in 1973 or later, who entered a D anish psychiatric hospital before 1994. Controls were drawn from a 10% samp le of the Medical Birth Register. Analysis was by logistic regression. Results. The risk of hospitalization for schizophrenia was 4.20 times highe r (95% CI = 2.4-7.4) for those born in Copenhagen versus those born in rura l areas of Denmark, and a linear relationship was demonstrated between urba nization of birthplace and risk. There was no difference in risk of hospita lization for affective psychosis for those born in Copenhagen versus rural areas. Obstetric complications had a moderate sized relationship to schizop hrenia, but the relationship of urban birth to schizophrenia was unaffected by adjustment for obstetric complications. Conclusion. Urban birth is a strong risk factor for schizophrenia, not medi ated by obstetric complications, which deserves further exploration. (C) 20 00 Elsevier Science B.V. All rights reserved.