ABSTRACT

Tramer first described a winter-spring excess of schizophrenic births in 1929.1 Since then, numerous studies from many countries have attempted to replicate the season-of-birth effect in patients with schizophrenia. Most of these studies found seasonality of birth in schizophrenic patients, predominantly in the months from December to May, with a peak in January and February. As for the magnitude of the birth excess, it ranges from 5-15%. In contrast, a smaller number of studies focused on months showing a deficit in schizophrenic births; that is, the months when individuals who develop schizophrenia are less likely to be born. The deficit period is in the summer and fall months, and the magnitude of this deficit in births has been reported to be greater than that of the excess births.2-5

Some have claimed the season-of-birth effect to be an artifact produced by factors such as age incidence and age prevalence effects.6 Like other earlier studies,2,4,5,7-14 two recent studies15,16 have been conducted to correct for such effects. Both of these studies clearly showed a winter-spring birth excess in schizophrenic patients even after allowing for these effects. Therefore, consensus has been reached among researchers that the winter-spring seasonal birth excess for schizophrenia is not an artifact, but a genuine phenomenon.