Obstetric complications and the risk of schizophrenia - A longitudinal study of a national birth cohort

Background: Numerous epidemiological studies found an increased risk of sch izophrenia among persons exposed to various obstetric complications. The un derlying mechansims are unknown. Objective: To study specific risk factors, as well as sets of risk factors, representing 3 different etiologic mechanisms: (1) malnutrition during fet al life; (2) extreme prematurity; and (3) hypoxia or ischemia. Methods: In this longitudinal cohort study, information in the National Bir th Register was linked to the National Inpatient Register. We followed up 5 07516 children born between 1973 and 1977 with regard to a diagnosis of sch izophrenia between 1987 and 1995 (238 cases). By record linkage, we also ha d access to data on psychiatric illness in the mother. Occurrence of schizo phrenia was measured by the Mantel-Haenszel test and logistic regression. Results: A number of specific risk factors were associated with an increase d risk of schizophrenia. The relative risk (95% confidence interval) for pr eeclampsia was 2.5 (1.4-4.5);vacuum extraction, 1.7 (1.1-2.6); and malforma tions, 2.4 (1.2-5.1). In logistic regression models, we found that indicato rs of all 3 etiologic mechanisms were associated with increased point estim ates of schizophrenia, although at lower risk levels. Preeclampsia, an indi cator of fetal malnutrition, was the only risk factor with statistically si gnificant increased risk after control for all potentially confounding fact ors. Conclusion: This study supports the theory of an association between obstet ric complications and schizophrenia. Although preeclampsia was the stronges t individual risk factor, there was evidence of increased risk associated w ith all 3 etiologic mechanisms.