Maternal hypotension is a common complication after spinal anesthesia for cesarean delivery (CD). Phenylephrine (PE) is the most popular vasopressor for prevention of post-spinal hypotension (PSH) during CD; however, the most appropriate protocol for PE administration is still unknown. The most common PE protocols used for prophylaxis against PSH are: single shot, fixed infusion, and variable infusion. A recent study reported that a dose of 1.5 mcg/Kg is the most suitable single-shot dose for prophylaxis. Another randomized controlled trial compared four doses of PE infusion and reported that 25 mcg/Kg/min and 50 mcg/Kg/min doses were the best doses for fixed infusion with accepted incidence of both PSH as well as reactive hypertension. Using variable infusion rate of PE had been recently introduced in another study with a starting dose of 0.75 mcg/Kg/min. The variable rate infusion showed very good results regarding PSH. In this study, the investigators will compare variable infusion of PE (at a starting rate of 0.75 mcg/Kg/min) with fixed rate (0.75 mcg/Kg/min which will stop if reactive hypertension occurred) and single shot protocol (1.5 mcg/Kg)