C. Rationale Progesterone as indicated in the Introduction has been shown in some, but not all, studies to reduce incidence of preterm delivery and the adverse effects of prematurity. Progesterone has been shown to reduce the number of oxytocin receptors in the myometrium and be responsible in the near term pregnant women for blocking the onset of labor. Weekly use of this compound, if effective, would be much superior to the tocolytic agents currently available.