Seasonality, birth complications and schizophrenia in a high risk sample.

It has been suggested that viral infections, more prevalent in the winter months, might increase pregnancy and birth complications, which might in turn be responsible for the excess of winter-born patients with schizophrenia. In this study it was found that the rate of schizophrenia among high risk winter-urban births who had suffered a perinatal complication was significantly greater than that for those who had not, thus supporting the hypothesis.