The ability of the MgSo4 as a neuro protectant is dependent on its cerebral vasodilating effects (Magee et.al,2011; Macdonald et.al, 2004), therefore we propose to measure the mean pulsility index (PI) and resistance index (PI) of the middle cerebral artery in the fetus twice, once before giving them the drug, and the other after 4 hours of starting the loading dose. All ultrasound and power doppler examinations will be carried out by the same investigator, using the Voluson 730 machine (GE Healthcare Austria GmbH, Seoul, Korea). Sample size calculation was done using Stats Direct statistical software version 2.7.2 for MS Windows, StatsDirect Ltd., Cheshire, UK.