If you had to choose only one remedy to using during labor, Arnica Formula for birth ARN would be it.
Take it throughout labor to prevent bruising—every 4 hours, or more frequently if it provides relief from pain. Typically, it will be more effective for those contractions that feel sore, bruised, aching—but manageable.
After labor, take 3-6 times daily for up to a week to speed the healing of bruised muscles and to help with after pains.
For more information on homeopathic remedies for child birth see Homeopathy.org