BACKGROUND The present study examines the effects of independent, single pre- and perinatal risk factors and rates of obstetric complications upon the subsequent development of schizophrenia.

METHOD This study was based on prospectively recorded birth records of 107 cases (82 with schizophrenic disorders and 25 with other psychotic reactions) and 214 controls, individually matched by gender and time and place of birth. Variables univariately associated with significantly elevated risk were entered in a logistic regression model.

RESULTS A high non-optimality summary score (> or = 7 complications of 34 possible) was a significant risk estimate for the total index group (OR 4.58, 95% CI 1.74-12.03) and the 82 schizophrenic patients (OR 3.67, CI 1.30-10.36). Patients with 2-6 complications also had an increased, although lower, risk (OR 1.67, CI 1.02-2.75). A disproportionate birth weight for body length (OR 3.57, CI 1.77-7.19) and a small head circumference (OR 3.93, CI 1.32-11.71) were the strongest independent risk factors.

CONCLUSIONS A contribution of obstetric complications to the risk of schizophrenia was confirmed. Only aberrations in physical size remained as individual independent risk factors.