Seasonality of schizophrenic births in the United States.

The birth months of persons later diagnosed as schizophrenic were studied. Data were collected from 19 states on 53,584 schizophrenics born between 1920 and 1955. The controls were the general births in the same states for the same years. A highly significant peak in schizophrenic births was found from December to May, most marked in March and April. The seasonality was stronger in New England and the Midwest than in the South. Previous studies of schizophrenic births are also reviewed. The cumulative evidence would appear to establish more firmly a winter and spring seasonality of schizophrenic births in northern Europe and the eastern United States. Selection of patients, nutritional factors, environmental factors, genetic factors, and infectious agents are discussed as possible etiological explanations.