With each uterine contraction, the mother experiences considerable pain. The cramping pain in early labor is probably caused mainly by hypoxia of the uterine muscle resulting from compression of the blood vessels in the uterus. This pain is not felt when the visceral sensory hypogastric nerves, which carry the visceral sensory fibers leading from the uterus, have been sectioned.
However, during the second stage of labor, when the fetus is being expelled through the birth canal, much more severe pain is caused by cervical stretching, per-ineal stretching, and stretching or tearing of structures in the vaginal canal itself. This pain is conducted to the motherâ€™s spinal cord and brain by somatic nerves instead of by the visceral sensory nerves.