About 15% of the population report experiencing delusions or hallucinations. It is not clear whether these experiences represent the first signs of things going wrong en route to schizophrenia or whether they simply reflect a variation in the way people perceive the world. Difficulties in pregnancy and around birth have been linked to the later development of psychosis and schizophrenia (in the children not the mothers) and a team of researchers from the University of Bristol looked into the links between these factors and psychosis-like symptoms in a sample of 6,356 12-year-olds. They found that psychotic symptoms were associated with maternal infection during pregnancy, maternal diabetes, a need for resuscitation and a child being in a poor state of health five minutes after birth. There was no association between psychotic symptoms and premature birth or pre-eclampsia.
Zammit, S. ... [et al] - Investigating whether adverse prenatal and perinatal events are associated with non-clinical psychotic symptoms at age 12 years in the ALSPAC birth cohort Psychological Medicine September 2009, 39(9), 1457-1467