Confinement of winter birth excess in schizophrenia to the urban-born and its gender specificity.
BACKGROUND
The season of birth phenomenon in schizophrenia was reexamined in relation to place of birth, in order to test the hypothesis that a seasonal factor might operate preferentially among those who were urban-born.


METHODS
The seasonal distribution of births was examined among 3253 patients in two case registers having an ICD-9 diagnosis of schizophrenia and compared with the distribution of births among the normal population born in those catchment areas over the same period; those subjects born in population centres greater than 50,000 were defined as urban-born.


RESULTS
Patients who were urban-born showed an excess of winter births relative to controls that was absent among their rural-born counterparts. On comparing patient groups, those who were urban-born were more likely to be born in the winter, while those who were rural-born were more likely to be born in the spring; this urban-rural distinction was confined essentially to female patients.


CONCLUSIONS
These findings might be accommodated most readily in terms of a spatially as well as seasonally varying environmental factor that is associated with urbanicity and to which female offspring are more vulnerable.
O'Callaghan
E
E
St John of God Psychiatric Services, Cluain Mhuire Family Centre, Dublin, Ireland.
Cotter
D
D
Colgan
K
K
Larkin
C
C
Walsh
D
D
Waddington
J L
JL
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011203:Poverty / Q000706:statistics & numerical data*; D012042:Registries / Q000706:statistics & numerical data; D012307:Risk Factors; D012424:Rural Population / Q000706:statistics & numerical data; D012559:Schizophrenia / Q000453:epidemiology* / Q000209:etiology; D012565:Schizophrenic Psychology; D012621:Seasons; D012737:Sex Factors; D014505:Urban Population / Q000706:statistics & numerical data*