Pregnancy and motherhood constitute periods of tremendous hormonal variation that orchestrate parturition, lactation, maternal care, maternal aggression, and recognition of offspring, among other functions. Cognitive processing also varies during pregnancy and motherhood and may serve an adaptive function in preparation for parturition and rearing. Additionally, maternal experience may have enduring consequences for the brain, behavior, and cognition long after offspring are mature. However, the early postpartum period also renders women psychologically vulnerable as approximately 15% of women experience postpartum depression, with estimates of 50-80% reporting a milder form of depression termed "maternal blues." This review will present literature on pregnancy- and parity-related changes in both cognition and affect and how these changes likely involve plastic changes within the hippocampus, a region that is sensitive to reproductive hormones. Further, this review will discuss steroid and peptide hormones that may contribute to affective and cognitive disruptions during pregnancy and postpartum. Research in this area may reveal insight into how pregnancy and motherhood alter the likelihood of developing postpartum depression and related disorders.