Seasons of birth and subtypes of schizophrenia.

Many studies show a higher rate of birth of schizophrenic patients during the winter and early spring months. This is particularly prominent in studies involving northern European countries and the northern part of the United States. The interpretations for this apparent seasonality remain highly speculative. We examined the seasons of birth of 472 patients carrying the diagnosis of schizophrenia. We also studied the gender and paranoid vs nonparanoid subtypes of this subject group. The total group does not show an excess of winter births. The same is true for total male (n = 193) and total female (n = 279) schizophrenic patients. The different subtypes of female patients show a homogenous distribution by seasons of birth; but the male paranoid schizophrenia group (n = 102) shows a significant increase of births during the first quarter of the year. The findings are interpreted according to the prevailing hypotheses of schizophrenia. The implications of these findings are discussed.