Prenatal and perinatal risk factors for schizophrenia, affective psychosis and reactive psychosis of early onset: case-control study

All Swedish children born during 1973-79 were involved in the study. Data from the Swedish birth register were linked with data from the Swedish inpatient register. The registers provide nationwide coverage for the study. Schizophrenia was positively associated with multiparity (odds ratio 2.0), maternal bleeding during pregnancy (odds ratio 3.5) and birth in late winter (odds ratio 1.4). Affective psychosis was associated with uterine atony (odds ratio 2.2) and late winter birth (odds ratio 1.5). Reactive psychosis was related to multiparity (odds ratio 2.1). An increased risk for schizophrenia was found in boys who were small for their gestational age at birth (odds ratio 3.2), who were number four or more in birth order (odds ratio 3.6) and whose mothers had had bleeding during late pregnancy (odds ratio 4.0).