| Summary: | Abstract The Northern Finland 1966 Birth Cohort is an unselected, population-based sample of 12,058 live born children. The present study is based on 10,934 individuals living in Finland at the age of 16 years. Ninety-six research diagnoses fulfilling operational DSM-III-R criteria for schizophrenia by age 34 years were found in the reassessment of clinical diagnoses. Of these 96 cases, 55 (57%) had concordant diagnoses (both the clinical and research diagnosis was schizophrenia) and 41 (43%) had discordant diagnoses (the clinical diagnosis was other than schizophrenia). Diagnostic discordance was associated with low parental social class in 1980, later age at onset, comorbid diagnosis of mental retardation, shorter treatment periods and lower number of treatment episodes. Unwanted pregnancy and parental history of psychosis increased the risk for schizophrenia. The combination of unwantedness of pregnancy and parental history of psychosis elevated the risk of schizophrenia over 8-fold in offspring compared to those without either risk factor. Both low and high birth weight increased the risk of later schizophrenia. Both short and tall babies also had elevated risk. A reverse J-shape curve described the associations between birth weight, length and schizophrenia. The ages when cohort members learned to stand, walk and became potty-trained were related to subsequent incidence of schizophrenia and other psychoses. Earlier milestones reduced and later milestones increased the risk in a linear manner. In conclusion, these results indicate that schizophrenia has complex phenomenology and developmental pathways. Its multiple symptomatology with no single specific defining feature and no absolute validation criteria makes the phenomenological-based diagnosis of schizophrenia challenging. Unwanted pregnancy may act as an additive factor for subjects already vulnerable to schizophrenia and psychoses may have a developmental dimension expressed as deviant foetal development and delayed milestones. These results support ...
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