More than 4 million births occur in the U.S. each year; in 2008, there were 4,247,694 births. The most commonly used labor pain management method in the U.S. is epidural analgesia. Use of inhaled nitrous oxide is a common option for labor pain management in several countries outside the U.S., including the United Kingdom, Finland, Sweden, Canada, Australia, and New Zealand. A significant barrier to use in the U.S. is limited availability of equipment to blend and deliver a mixture of nitrous oxide and oxygen for self-administration by laboring women. Nitrous oxide, sometimes called "laughing gas" because it can produce euphoria, is an inhalational anesthetic and analgesic gas. Nitrous oxide has been used in dental care since the mid-1800s and is commonly used for this indication today. Use of nitrous oxide during labor began in the late 1800s, and equipment for self-administration was introduced by Minnitt in England in 1934. The mechanism of action of nitrous oxide is thought to be an increased release of endorphin, dopamine, and other natural pain relievers in the brain, which modulate pain stimuli via descending spinal cord nerve pathways. Nitrous oxide does not completely relieve the pain of labor but creates "diminished pain, or a continued awareness of pain without feeling bothered by it." Nitrous oxide also has an antianxiety effect, which may be helpful if laboring women are restless and doubt their ability to cope, emotions that are not uncommon, especially during transition. A variety of pain management methods were described in studies in this review. Epidural analgesia is the most commonly used method in the U.S. and may block pain entirely. Although nitrous oxide would not be expected to be as effective for analgesia as an epidural because of the differences in their mechanism of action, nitrous oxide has other benefits, including its lower cost and less invasive nature. Nitrous oxide has a rapid onset and end of action. Most women in the U.S. use some type of medication for labor pain management. However, the option of using nitrous oxide to relieve labor pain is limited by its lack of availability. Use of nitrous oxide during labor is common in other countries, increasing interest in this method in the U.S., in part because it is less expensive and invasive than widely used regional anesthesia. This review attempts to assess the effectiveness of nitrous oxide in managing labor pain and to identify potential factors that may influence its availability and use within the U.S. The primary questions include the comparative effectiveness of nitrous oxide for the management of labor pain, the influence of nitrous oxide on women's satisfaction with their birth experience, the health system factors influencing its use within the U.S., and any adverse effects associated with this intervention. Key Questions include: 1. What is the effectiveness of nitrous oxide when compared with other methods for the management of labor pain among women intending a vaginal birth? 2. What is the comparative effectiveness of nitrous oxide on women's satisfaction with their birth experience and pain management? 3. What is the comparative effectiveness of nitrous oxide on the route of birth? 4. What is the nature and frequency of adverse effects associated with the use of nitrous oxide for the management of labor pain, including but not limited to: Maternal adverse effects, such as nausea and vomiting, dreams, dizziness, unconsciousness, and postpartum complications. Fetal/neonatal adverse effects, such as low Apgar scores and abnormal fetal cord blood gases. Childhood adverse effects, such as drug dependency and developmental complications. Adverse effects on health care providers and other individuals present for labor. 5. What are the health system factors influencing the use of nitrous oxide for the management of labor pain, including but not limited to provider preferences, availability, setting, and resource utilization?