The role of obstetric events in schizophrenia.

It is now well established that obstetric complications or obstetric events increase the risk for schizophrenia. This is a small effect—the pooled odds ratio of the effect of exposure to obstetric complications on the subsequent development of schizophrenia has been estimated to be about 2.0 (95% confidence interval, 1.6–2.4). The term ‘‘obstetric complications’’ covers a wide range of events, and for many years researchers have tried to tease apart this association in order to identify the one complication or underlying mechanism that is responsible for the increase in risk. Results from large population-based studies have been pooled to give substantial sample sizes for meta-analysis. Yet no one unifying mechanism has emerged. The most parsimonious approach at present may be to group complications of apparently similar modes of action together. The three ‘‘groups’’ that have emerged from the literature to date are (a) fetal growth retardation, (b) fetal perinatal hypoxia, and (c) prenatal complications.