What We Already Know

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).1–3 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 compli-cation 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 simila