A. Introduction Preterm birth occurs in 7-12% of all deliveries, but accounts for over 85% of all perinatal morbidity and mortality.1 Despite many strategies for reducing the incidence of preterm birth none have been totally effective. One treatment that showed promise in earlier small trials was the prophylactic administration of progestational compounds.2,3 However, the reports of efficacy were mixed with some showing benefits4,5 while others did not.6,7 More recently, two randomized clinical trials have shown great promise8,9, and revealed a significant decrease in preterm births among women who received 17 alpha-hydroxyprogesterone caproate (17P)8, or 100mg of progesterone delivered by vaginal suppository per week.9 Indeed support by the American College of Obstetricians and Gynecologists, and March of Dimes as well as others have made this treatment the standard of care in many areas of the country.