Preterm birth (PTB) remains a major cause of neonatal mortality and morbidity, despite improvements in tocolytic treatment and neonatal care. Progesterone (17a-hydroxyprogesterone) produced naturally or synthetically can prevent PTB when applied vaginally and orally. Progesterone use may be a safe and cost-effective option in cases of singleton pregnancy with prior PTB, asymptomatically short cervix and arrested preterm labor.