Continuous labor support provided by professional doulas is associated with improved birth outcomes for pregnant women and their infants. However, there is limited data on the impact of using female relatives as lay doulas. This systematic review included nine published studies that examined the association between use of female relatives as lay doulas with childbirth outcomes. In some study populations, there was a decrease in the number of cesarean births and length of labor, and in all studies, there was improved maternal birth satisfaction. However, the woman's chosen female relative often did not receive education regarding labor support skills before providing continuous support. Educational programs designed to teach labor support skills to female relatives are needed.