“…Pain during the first stage of labor reflects activity in the hypogastric nerve, as evidenced by its relief by paracervical injection of local anesthetic, 1 and reflects primarily activation of nerves innervating the lower uterine segment and cervix, as evidenced by reproduction of labor pain by manual distension of these structures, but not the uterine fundus. 2 In rats, distension of the lower uterine segment and cervix increases firing of afferents in the hypogastric nerve, 3 and activates neurons in the thoraco-lumbar spinal cord dorsal horn 4 with a pattern similar to that observed with labor and delivery in this species.…”