The HPA axis involves interactions among the hypothalamus, anterior pituitary, and adrenal cortex. Genes that are critical to the HPA pathway include, Brain-derived neurotrophic factor (BDNF), FK506 binding protein 5 (FKBP5), Corticotropin-releasing hormone/factor (CRF/CRH), and Glucocorticoid receptor (NR3C1). Ultimately, the HPA axis cascade results in the production of cortisol, which has the potential to cross the placental barrier. Cortisol has been shown to regulate fetal readiness for birth and infant survival. HPA-axis associated genes are also involved in trophoblast growth and proliferation as well as nutrient transport.