There are a number of critical windows during prenatal and postnatal life and a range of potential agents including exposure to maternal and fetal stressors, nutrition, and antenatal administration of synthetic glucocorticoids and postnatal maternal care and behaviour that are important in programming the subsequent reactivity of the HPA axis. Recently, it has become clear that the periconceptional period is also an important critical period during which changes in the level of maternal nutrition result in altered development of the fetal HPA axis. These findings have potential implications for the ability of the fetus to respond to acute and chronic stressors, for the timing of parturition and have potential implications for adult cardiovascular and metabolic health outcomes. In this review we focus on the different models which have been used to investigate the impact of maternal undernutrition during the periconceptional period on the prepartum activation of the fetal HPA axis. We propose that the term "periconceptional" should be used to refer to the developmental stages which include some or all of the following early events: oocyte maturation, follicular development, conception, and embryo/blastocyst growth up until implantation. When maternal undernutrition extends beyond implantation, up until early placentation, then it is appropriate to describe maternal undernutrition as occurring during 'early gestation'. Further work is required to define the relative contributions of nutritional factors operating in the periconceptional and early gestational periods on the programming of the subsequent development of the HPA axis and is of importance for fetal, postnatal and subsequent adult cardiovascular and metabolic health.