Placenta previa is implantation of placenta on or near internal os .It is classified into major degree when lower edge of placenta lies within 2 cm from internal os , and minor degree if lower edge of placenta at lower uterine segment but more than 2 cm from internal os .~There are many risk factors for developing placenta previa including multi parity , multiple pregnancy , increased maternal age (>35y ) , previous uterine surgery , history of placenta previa (4-8%) .~A significant degree of uterine contractility has been observed with symptomatic placenta previa. It is directly associated with vaginal bleeding. However, a large percentage of women who have placenta previa associated with haemorrhage will experience subclinical uterine contractions before the onset of overt vaginal bleeding. Therefore, the use of tocolytic agents in management of placenta previa seems reasonable .~Magnesium sulfate alters calcium up take, binding and distribution in smooth muscles of the uterus, so reduces the frequency of cell depolarization and inhibits myometrial contraction .~In addition to its tocolytic action magnesium sulfate also provide neuroprotection to preterm infant . .~At women Health Hospital, Assiut University, Egypt our policy is using magnesium sulfate as first line for tocolysis for placenta previa patients with preterm uterine contractions. By giving a loading dose of 4 g on 150 ml saline intravenous infusion over 20 minutes, and a maintenance dose of 6g/6h on 500 ml saline slow intra venous infusion
To assess the efficacy and safety of alternative magnesium sulfate regimens when used as single agent tocolytic therapy for prevention of preterm labour in patients with symptomatic placenta previa and subsequent changes in the cervical length .