Background: Preeclampsia is a disease that commonly develops during the 2nd half of pregnancy. There were many attempts to test a variety of biological, biochemical and biophysical markers to predict the occurrence of the disease, but so far there is no reliable screening tests for that as well as no prevention measures could be efficacious for the disease. Doppler ultrasound is considered one of the most important tools for assessment of fetal wellbeing through applying Doppler velocimetry studies on the umbilical artery. Objective: To compare between umbilical artery Doppler indices (resistance index, pulsatility index and the systolic/diastolic ratio) before and after use of loading dose of magnesium sulfate over 20 minutes in pregnant women with severe preeclampsia, and the possible effects of such changes on the mode of delivery and neonatal outcome. Patients and Methods: A prospective observational cohort study in 100 pregnant women was conducted at the Obstetrics and Gynecology Department, Al-Galaa Teaching Hospital. Cases were recruited from the emergency unit during the period from November 2019 to July 2020. Doppler ultrasonography of the umbilical artery underwent before and after intravenous administration of 6 g of magnesium sulfate (loading dose) over 20 minutes. The variables studied were the Doppler velocimetry parameters of the umbilical artery. The comparison of means between the measurements (before and after) of each individual was performed. Results: There was a significant difference between umbilical artery resistance index (RI) before, and 20 minutes after administration of the loading dose of MgSO4. It was found that the loading dose of MgSO4 elicited a slight reduction in umbilical artery resistive index (RI) from before taking it and 20 minutes after (0.69 ± 0.05 vs 0.65 ± 0.05). There was a significant difference between umbilical artery pulsatility index (PI) before, and 20 minutes after administration of the loading dose of MgSO4. There was a statistically highly significant difference of means of umbilical artery Doppler indices after magnesium sulfate. Magnesium sulphate did not affect the neonatal Apgar score, and the need for resuscitation and intensive care unit (ICU) admission. Conclusion: Intravenous administration of magnesium sulfate in pregnant women with severe preeclampsia resulted in a reduction in umbilical artery Doppler indices with reduced resistance to blood flow in these vessels.