Background: Spontaneous preterm labor (SPTL) and preterm birth (PTB), is the single most important cause of perinatal mortality and morbidity in high-income countries despite the enormous efforts over the past several decades. Preterm labor is defined as regular, painful, frequent uterine contractions causing a progressive effacement and dilatation of the cervix occurring before 37 completed weeks of gestation. Many drug therapies were used as tocolytics in cases of preterm labor, however none of them proved to be the best. The present study was performed to compare three of the used drugs for tocolysis to assess their efficacy and side effects on the mother and fetus. Aim: The aim of this study is to compare the effect of oral nifedipine, intravenous ritodrine infusion and magnesium sulfate infusion used as tocolytics in cases of preterm labour on Doppler parameters of fetal umbilical and middle cerebral artery and to evaluate their effects on the mother and the fetus in order to choose the safest and the most effective drug. Methodology: This study was held in the period from December 2014 to october 2015 on 90 patients attended and admitted from the Casualty Unit of the Obstetric Department In Elsayed Glal University Hospital with preterm labor pains , intact membranes, singleton pregnancy between 28 and completed 34 weeks gestation. All patients had been dated accurately with a gestational age based on the last menstrual period and if available a corresponding second trimester ultrasound report performed before 20 weeks gestation. Treatment continued until contractions stopped for 24 hours, maximum doses were attained without response; unacceptable side effects occurred or labor proceeded. Successful treatment was defined as cessation of contractions observed for 24 hours and no further cervical changes. Patients with successful treatment were put under observation for another 24 hours without additional treatment then discharged on no maintenance therapy. Results: Maternal tachycardia, palpitation and dyspnea were more common in the ritodrine group with (p-value = 0.000). The present study showed increase in umbilical artery PI after treatment in the magnesium sulfate group only which was statistically significant (P value = 0.016). The study showed statistically significant increase in middle cerebral artery PI after treatment in magnesium sulfate group with a P value=0.000 and statistically significant decrease in middle cerebral artery with nifedipine group with P value=0.027. When comparing the cerebroplacental ratio before and after treatment in the three groups; the study showed significant increase in cerebroplacental ratio after treatment in the magnesium sulfate group with P value = 0.000, which is statistically significant. This suggests that nifedipine could be used as a safer alternative to ritodrine and magnesium sulfate. Conclusion: In our study, nifedipine therapy was not associated with a significant change in maternal systolic and diastolic blood pressure after 24h, with minor insignificant effect on maternal heart rate. Fetal heart rate was not affected after therapy. Fetal Doppler study found no clinically significant effect on the pulsatility index (PI) of umbilical and middle cerebral artery, while with magnesium sulfate therapy there was increase in cerebro- placental ratio 24hr after treatment, these findings ensure safety of the drugs on the maternal and fetal aspects.