Discrimination between two competing hypotheses on seasonality of birth in subfecundability traits

In order to explain the winter (and often summer) birth excess of women characterized by subfecundity two competing hypotheses have been proposed: i) the seasonal preovulatory overripeness ovopathy (SPrOO) hypothesis (1-3) and ii) the epidemic seasonal infertility factors (ESIFs) hypothesis (4-6). The former assumes nonoptimum maturation of the oocyte during the seasonal transitions in the mother due to inappropriate hormonal feedback, comparable with other conditions in maternal reproductive life, e.g. menarche, menopause, postpregnancy restoration of the ovulation rate, etc. The latter assumes seasonal epidemic pathogens during the mother's pregnancy, or later in life. Agreement, disagreement and discrimination between these competing hypotheses were evaluated. The SPrOO hypothesis appears to have the virtue of raising several testable predictions and of offering more explanatory power. In addition, it incorporates the main stream of knowledge about congenital anomalies and elucidates many constitutional and reproductive enigmas in human reproduction.