Excess seasonality of births among patients with schizophrenia and seasonal ovopathy.

In this study we examined whether the well-known winter excess of schizophrenic births exists among Dutch schizophrenia patients when statistical artifacts such as the age-incidence and age-prevalence effects are avoided and, if so, whether the seasonal preovulatory release of overripe ovum (SPrOO) hypothesis, that is, seasonally bound ovopathy, might be an explanation for this excess. We analyzed the month-of-birth distribution of 1,037 Dutch schizophrenia patients born between 1962 and 1966 and first admitted to a psychiatric hospital between 1978 and 1990 by the so-called window analysis to avoid the artifacts mentioned. The results show a winter excess of births among Dutch schizophrenia patients, even when statistical artifacts are avoided, and that the SPrOO hypothesis might be an explanation for this excess. Further research is needed to support the hypothesis that ovopathy, either seasonally bound or not, could be involved in the etiology of schizophrenia.