I believe the answer is Corticotrophin releasing hormone. Corticotropin-releasing hormone is a peptide hormone involved in the stress response. It is a releasing hormone that belongs to corticotropin-releasing factor family. Its main function is the stimulation of the pituitary synthesis of ACTH, as part of the HPA axis. The Corticotropin releasing hormone derived from the placenta is secreted into the maternal circulation in large amounts during the third trimester of human pregnancy and may have an important role in the onset of labor.
