Background: Preterm delivery is labor beginning before completing 37 weeks of gestation with progressive effacement and dilatation of the cervix in the presence of regular painful contractions. Preterm labor as one of the biggest challenges for obstetricians is a world health problem and is responsible for approximately two-thirds of early neonatal morbidity and mortality. Objectives: To compare the effectiveness and safety of nifedipine therapy versus combined use of vaginal progesterone and nifedipine as acute tocolysis and their effect on maternal and fetal blood flow measured at 24 and 72 hours after their use. Patients and Methods: This prospective randomized observational comparative clinical study included 52 pregnant women with symptoms and signs of preterm labor that were randomly allocated into two groups each group consisted of 26 patients. This study was conducted in Obstetrics and Gynecology Department, Menoufia University Hospitals in the period between March 2019 and March 2020. Their gestational ages ranged from 28-34 completed weeks.  Result: Time interval between last epilat capsules to tocolytic effect in minutes was significantly shorter in group B than in group A. There was no significant difference between the two groups in Doppler parameters with no long-term effect on fetomaternal circulation as tocolytics in acute preterm labor. Conclusion:  This study concluded that oral nifedipine plus vaginal progesterone is associated with more rapid response to tocolysis in threatened preterm labor compared to oral nifedipine alone with nearly the same effect on maternal and fetal blood flow.