Genetic and environmental factors involving familial antecedents and prenatal development have been described to increase risk of schizophrenia and to bring forward age at onset.

To evaluate the relationship between age at onset of psychosis (AOP) and parents age and antecedents, OCs and weight and gestational age at birth in patients with a first episode of psychosis.

90 patients with first-episode psychosis were included. Socio-demographic characteristics, clinical variables and drug use were assessed through a questionnaire using the Structured Clinical Interview for DSM (SCID). Family history of psychosis was assessed through the Andreasen interview and OCs were measured using the Lewis and Murray Obstetric Complication Scale. Also age of parents at patient's birth, miscarriages previous to patient's birth, mother's use of drugs during pregnancy and weight and gestational age at birth were investigated.

An earlier AOP was significantly related to earlier use of stimulating drugs (p 0.044), paternal antecedent of psychosis (p 0.044), pre-eclampsia (p 0.000), use of forceps (p 0.001) and need of incubator at birth (p 0.000). Also birth weight was positively related to AOP (r 0.297, p 0.015). Other significant relationship of AOP with obstetric and family variables or drug use were not found.

These findings are consistent with previous studies results which had found association between OCs and low birth weight and AOP. Previous and current results underline the role of the prenatal period in the development of schizophrenia and the importance of careful monitoring of pregnancies of mothers with psychotic disorder.