Background. Many studies have suggested a possible aetiological role for obstetric complications in the development of schizophrenia. We focused on prenatal physical growth in schizophrenia, a contentious issue in the literature.

Methods. We compared gestational age at birth, birth weight (BW) and birth head circumference (BHC) between 312 schizophrenics and 517 controls, and between 187 schizophrenics and their matched healthy siblings. Information on obstetric histories was obtained from the Maternal and Child Health Handbooks (i.e. contemporaneous records).

Results. Gestational age at birth was significantly earlier in the schizophrenics than in the controls (P = 0·017). Pre-term birth (gestational age of 36 weeks or less) was more common in schizophrenics than in controls (8·0% v. 3·4%, P = 0·005, odds ratio 2·5). Low BW (2500 g or less) was more frequent in schizophrenics than in controls (9·6% v. 4·6%, P = 0·005, odds ratio 2·2). The schizophrenics had significantly lighter BW (P = 0·0003) and tended to have smaller BHC (P = 0·081) compared with controls. However, multiple regression analysis showed that there was no significant difference in BW or BHC between the schizophrenics and controls when gestational age and maternal weight were controlled. There was no significant difference in BW or BHC between schizophrenics and their siblings, although the schizophrenics tended to be born at earlier gestational age than their siblings.

Conclusions. Our results suggest that prematurity at birth is associated with a risk of developing schizophrenia in adulthood. When gestational age and maternal body weight were allowed for, there was no evidence that schizophrenics tend to have lower mean BW or smaller BHC.