Most common interventions recommended to prevent preterm birth, such as bed rest, tocolytics, antibiotics and cervical cerclage have been proven to have little or no benefit.8 Once preterm labor is established, the goal of treatment is merely to delay delivery in order to allow for the transfer of the pregnant patient to the most appropriate hospital and for administration of corticosteroids.11 None of the currently available treatments for preterm labor can prolong pregnancy sufficiently to allow further intrauterine growth and maturation of the fetus.12 There is experimental support from animal and in vitro studies, and also empirical evidence from large randomized placebo-controlled clinical trials, that treatment with progestins may reduce the risk of preterm birth in both high-risk asymptomatic patients and in those presenting with signs and symptoms of preterm labor. Progestins are a group of steroid hormones that include natural progesterone and its analogs, such as 17 alpha hidroxyprogesterone caproate (17P) and medroxy progesterone acetate (MPA).