Pain during the first stage of labor is generated largely from the uterus. Visceral sensory fibers from the uterus, cervix, and upper vagina traverse through the Frankenhauser ganglion, which lies just lateral to the cervix, and enter into the pelvic plexus and then into the middle and superior internal iliac plexuses. From there, the fibers travel in the lumber and lower thoracic sympathetic chains to enter the spinal cord through the white rami communicantes associated with the T10 through T12 and L1 nerves. Early in labor, the pain of uterine contractions is transmitted predominantly through the T11 and T12 nerves.