IRCT201710079014N192 IRCT 2017-10-09 Vice-chancellor for Research and Technology, Hamadan University of Medical Sciences Effect of oral progesterone versus placebo on reducing preterm labor in women with a history of preterm labor Effect of oral progesterone versus placebo on reducing preterm labor in women with a history of preterm labor: a double blind randomized clinical trial 2017-01-20 anticipated 214 Complete https://irct.ir/trial/9630 interventional Randomization: Randomized, Blinding: Double blinded, Placebo: Used, Assignment: Parallel, Purpose: Treatment, Other design features: Randomization: Random assignment of the patients to the intervention and control groups through drawing of lots. Blinding: Patients will be unaware of the type of intervention. The physician who will examine the patients will not be aware of the intervention. Therefore, the trial will be run as double blind. 1-2 Preterm labour. Intervention 1: Intervention group: Oral capsule medroxyprogesterone 100 mg twice a day until 36 weeks of pregnancy. Intervention 2: Control group: Oral capsule placebo twice a day until 36 weeks of pregnancy.