Obstetric factors, urbanization and psychosis.

BACKGROUND: Epidemiologic evidence as early as the 1930s has suggested urbanization is linked to schizophrenia, either by place of admission, place of upbringing, or, more recently, place of birth. In the past decade, obstetric complications have been implicated in the etiology of schizophrenia.
METHODS: With appropriate protections for anonymity, the files of the Danish Medical Birth Register were linked with the files of the Danish Psychiatric Case Register. The linkage produced 132 cases of schizophrenia and 69 cases of affective psychosis, who were born in 1973 or later, who entered a Danish psychiatric hospital before 1994. Controls were drawn from a 10% sample of the Medical Birth Register. Analysis was by logistic regression.
RESULTS: The risk of hospitalization for schizophrenia was 4.20 times higher (95% CI=2.4-7.4) for those born in Copenhagen versus those born in rural areas of Denmark, and a linear relationship was demonstrated between urbanization of birthplace and risk. There was no difference in risk of hospitalization for affective psychosis for those born in Copenhagen versus rural areas. Obstetric complications had a moderate sized relationship to schizophrenia, 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 mediated by obstetric complications, which deserves further exploration.