postpartum period. For example, pregnancy-related steroid hormones and peptides, such as oxytocin, dampen the reactivity of the HPA axis during pregnancy. Furthermore, there is evidence that cortisol, adreno-cortico-tropic-hormone, corticotropin releasing hormone, and corticosterone binding globulin (CBG) levels are altered significantly during pregnancy and postpartum. For example, stress hormone levels rise during pregnancy, reach a peak before birth, and drop after birth in rats and humans [45]. Based on this fact, corticosterone has been used to establish a PPD animal model [27]. In summary, the postpartum period is a time of increased vulnerability to depression which may be due to the dramatic fluctuations of gonadal and adrenal hormones that deserve special attention and consideration. However, more research is needed to better understand the causes and contributing factors for depression during postpartum.
