Excess in the spring and deficit in the autumn in birth rates of male schizophrenic patients in Italy: potential role of perinatal risk factors.

Objective: The aim of this study was to evaluate whether there were different seasonal variations of births in an Italian population of patients with schizophrenia, with other psychotic disorders, and with personality disorders than in the general population.

Methods: Birth dates of 1270 patients admitted to one university psychiatric unit in Rome between 1990 and 2003, with a diagnosis of schizophrenia, other psychotic disorder (OPD) and personality disorder/cluster A (PD) were analyzed according to seasonal variation.

Results: A significant excess of births in spring (with a peak in May) and a deficit in autumn (with a trough in October) was found in the sample of male schizophrenics (n = 506). No statistically significant variations were found in either the sample of female schizophrenics (n = 88) or in the combined sample with OPD and PD (n = 676).

Conclusions: The findings serve to strengthen the existing hypotheses that schizophrenia is related to environmental factors acting on the development of the central nervous system intrauterinely.