Abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis is an important pathological finding in pregnant women exhibiting major depressive disorder. They show high levels of cortisol proinflammatory cytokines, hypothalamic-pituitary peptide hormones and catecholamines, along with low dehydroepiandrosterone levels in plasma. During pregnancy, the TH2 balance together with the immune system and placental factors play crucial roles in the development of the fetal allograft to full term. These factors, when altered, may generate a persistent dysfunction of the HPA axis that may lead to an overt transfer of cortisol and toxicity to the fetus at the expense of reduced activity of placental 11β-hydroxysteroid dehydrogenase type 2. Epigenetic modifications also may contribute to the dysregulation of the HPA axis. Affective disorders in pregnant women should be taken seriously, and therapies focused on preventing the deleterious effects of stressors should be implemented to promote the welfare of both mother and baby.Keywords: brain; depression; neuroendocrine; pregnancy; stress; glucocorticoids Extensive studies have demonstrated that early life stressors produce changes in behavior and enhance the sensitivity of the stress response systems [1][2][3][4] . Although the genetic background has been implicated in the development of mood-related disorders, and genetic research has identified some chromosomal regions and genes that are involved in susceptibility to mood disorders, the etiology of anxiety and depressive disorders is still not clear in humans, particularly in women with major depressive disorder (MDD) [1] .The pathogenesis of perinatal depression is an emerging field. Although considerable progress has been made in this area in the last few years, there still remain unanswered questions and gaps in our knowledge of the underlying pathogenesis, the long-term impact of perinatal depression on the developing fetus, and the best methods for counseling pregnant women concerning the risks of untreated MDD versus the risks of psychopharmacologic treatment during pregnancy and lactation [5] . Meta-analysis studies have reported that the mean prevalence rate of prenatal depression is ~12% (this varies greatly according to location, mode of assessment, and socioeconomic conditions), and show that a large percentage of pregnant women displaying major depression remain depressed in the postpartum period and/or continuously [6,7] . Anxiety, depressive disorder, and stress during pregnancy are risk Phillipe Leff Gelman, et al. HPA axis in perinatal depression 339 factors for negative outcomes in newborns, like preterm birth or low birth weight; also, insecure attachment and impaired child development could be a consequence of mental disorders during pregnancy [6,[8][9][10] . The mechanisms by which maternal depression impacts fetal and neonatal development are currently under investigation; there is some evidence that depressive symptoms impact the infant's hypothalamic-pituitary-adrenal (HPA) axis, enhancing the ...