Gender-specific decline and seasonality of births in operationally defined schizophrenics in Italy.

All clinical records of schizophrenic patients included in the period 1979-1995 in the South Verona Psychiatric Case Register were reviewed and diagnoses operationally defined according to ICD-10 criteria using OPCRIT 3.1. Among the 335 scrutinized, 205 patients met the ICD-10 criteria for paranoid or undifferentiated schizophrenia. No seasonality of birth was found in these patients using a log-linear equiprobability model. The incidence and seasonality of birth were then analysed on the subsample of 106 patients born in 1947-1974 for whom corresponding data for the Verona general population were available. Schizophrenic males displayed a significant excess of birth in November-January with respect to the Verona population (chi 2 = 10.93, p = 0.012). The time series of the incidence of schizophrenia by cohort of birth 1947-1974 had a linearly decreasing trend, steeper in males than in females. The significant increase in age at first ever psychiatric contact, observed in both males and females throughout the period considered, cannot completely account for the gender-specific decline of birth of schizophrenics.