What agent should be used to prevent recurrent preterm birth: 17-P or natural progesterone?

Preterm birth has increased over the last decade. In 2006, 12.5% of all births in the United States occurred at fewer than 37 weeks gestation. This is associated with significant health care costs as well as related neonatal morbidity and mortality. In 2003, costs related to care for infants with preterm-birth or low-birth weight exceeded 11 billion dollars. This article reviews the literature on 17 alpha-hydroxyprogesterone caproate (17-P) and natural progesterone and concludes that 17-P is indicated for prevention of preterm birth in women with a documented history of a preterm birth before 37 weeks.