Preterm birth is one of the leading causes of neonatal morbidity and mortality. One of the most significant risk factors is a history of a prior spontaneous preterm birth. Intramuscular progesterone is the only FDA approved medication for the prevention of recurrent preterm birth. Vaginal progesterone is not FDA approved for the prevention of recurrent preterm birth, but has been found to beneficial. Given the presence of trials demonstrating efficacy for both intramuscular and vaginal progesterone in the prevention of recurrent preterm birth, but limited information one being more superior to the other, we are performing a trial comparing vaginal progesterone and intramuscular progesterone for the prevention of recurrent spontaneous preterm birth in women with a history of prior spontaneous preterm birth.