Background: Spontaneous preterm labor (SPTL) and preterm birth (PTB) is defined as birth before 37 completed weeks, and is the single most important cause of perinatal mortality and morbidity in highincome countries. Ritodrine is a betasympathomimetic drug that is frequently used for the prevention of preterm birth. One of the most important side effects of ritodrine is pulmonary edema. The lower incidence of side effects in comparison with ß-agonists undoubtedly has been the prime incentive to start the use of calcium channel blockers for tocolysis. The side effects also appear to have less impact on maternal wellbeing and are of shorter duration. Contrary to ritodrine, nifedipine had minimal effects on maternal pulse rate, systolic and diastolic blood pressure, serum potassium concentrations and blood glucose levels. Objective: To assess and compare the effects of nifedipine, ritodrine and magnesium sulfate on Doppler parameters of fetal umbilical and middle cerebral artery in cases of preterm labor. Patients and methods: A prospective cohort study conducted on pregnant women in the department of Obstetrics and Gynecology of Al-Ayat Central Hospital. A total of 150 cases coming to the casualty unit with preterm labor pains had been included in the study. Patients had been divided into 3 equal groups: Group A received intravenous ritodrine infusion, Group B received oral nifedipine, and Group C received intravenous magnesium sulfate infusion Results: There was no statistically significant difference between groups regarding to demographic data. Bishop score before and after treatment. However, there was a statistically significant difference between groups according to maternal heart rate after treatment. Also, significant difference between before and after treatment according to maternal heart rate in ritodrine group. There was no statistically significant difference between groups regarding to contraction frequency at starting and at maintenance tocolytic, time from starting the drug till delivery, failure rate and cessation of contractions but there was a statistically significant difference between groups regarding to stopping the drug due to side effect. According to fetal umbilical artery PI in magnesium sulfate, group C showed significant difference between before and after the treatment. Also, significant difference between before and after treatment according to fetal middle cerebral artery PI in nifedipine (group B), and magnesium sulfate group (group C). There was a significant difference between before and after treatment according to cerebroplacental ratio in magnesium sulfate group (group C). Conclusion: There was no overall difference between ritodrine, nifedipine, and magnesium sulfate in their efficacy as tocolytic for preterm labor. In addition, it showed that the maternal side effects profile was fewer with nifedipine and magnesium sulfate than with ritodrine.