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.