Previous studies of the maternity blues have failed to identify a consistent factor discriminating between the group of women who experienced the phenomenon and those who did not. The present study hypothesized that the maternity blues are a hormonally-assisted grief reaction which will occur predominantly in women whose antenatal expectation of baby or delivery fails to be fulfilled by the reality events. The hypothesis was tested in a prospective study of 89 women. The phenomenology of the blues was not found to be associated with the hypothesized sense of disappointment or anti-climax despite many womens' experiences falling short of expectation. Rather, the most powerful predictor of the blues was a sense of "pessimism" in late pregnancy which was actually fulfilled by postpartum reality. In addition, the triad comprising of severity of pre-menstrual tension, unplanned pregnancy and consideration given to elective termination in early pregnancy was associated with increased incidence of the blues.