Vaginal Progesterone for the Prevention of Preterm Birth in Women With Arrested Preterm Labor

Preterm birth, defined as birth before 37 weeks' gestation, is a leading cause of infant death and disease. Progesterone is the single most effective intervention in the prevention of preterm birth. However, current use of this therapy is limited to certain high-risk groups including women with a history of preterm birth and women with a short cervix. This study seeks to evaluate the efficacy of this preventive therapy in another high-risk group: women with arrested preterm labor. The investigators hypothesize that administration of vaginal progesterone in women who present with preterm labor but remain undelivered 12 hours after cessation of short-term therapy to inhibit contractions will result in lower rates of preterm birth before 37 weeks' than will administration of placebo.