Aim: to determine the prevalence of OHSS and clinical outcomes in high-risk women undergoing ART following calcium IV infusion. Methods: Double-blinded randomized controlled trial included two hundred women at risk to develop OHSS undergoing IVF/ICSI treatment cycle subdivided randomly into two equal groups; group I (intervention group (study/calcium infusion group, n=100) received intravenous infusion of 10 mL 10% calcium gluconate in 100 mL 0.9% saline solution on the day of ovum pick-up (OPU) and days 1, 2, and 3 after, and group II (control/placebo group, n=100) received 100 mL 0.9% saline solution on the day of OPU and days 1, 2, and 3 after. Main Outcome Measure: Incidence of OHSS. Results: OHSS incidence was significantly lower in the calcium infusion group (group I) than in the placebo group (group II): 8 (8%) vs. 26 (26%); moderate OHSS was significantly lower in group I than in group II: 3 (3%) vs. 10 (10%); and severe OHSS was significantly lower in group I than in group II: 0 vs. 4 (4%). Conclusion: IV calcium infusion has a significant preventive role against OHSS without adverse effect on pregnancy outcomes.