The modern domestic sow exhibits a period of impaired reproductive performance known as seasonal infertility during the late summer and early autumn months. A reduction in farrowing rate due to pregnancy loss is the most economically significant manifestation of this phenomenon. Presently, little is known of the aetiology of seasonal pregnancy loss in the pig. Recent findings represent a major advancement in the understanding of sow reproductive physiology and implicate poor oocyte developmental competence as a contributing factor to pregnancy loss during the seasonal infertility period. It has also been demonstrated that ovarian activity is depressed during the seasonal infertility period. The reduction in oocyte quality is associated with decreased levels of progesterone in follicular fluid during final oocyte maturation in vivo. The recent identification of sow-specific risk factors, such as parity for late pregnancy loss, should improve breeding herd efficiency by allowing producers to tailor management interventions and/or culling protocols that target animals identified as having a greater risk of late pregnancy loss during the seasonal infertility period.