Aim: To compare effectiveness of calcium infusion (CI) versus oral cabergoline (OC) in lowering the incidence and severity of ovarian hyperstimulation syndrome (OHSS) in high risk women undergoing in vitro-fertilization (IVF)/intracytoplasmic sperm injection (ICSI) cycles. Patients and methods: This trial was conducted at Benha University Hospital and Hawaa specialized infertility center, including 230 women undergoing ICSI, 115 women received intravenous Calcium gluconate starting at ovum pick up (OPU) day and 115 women received OC 0.5 mg starting at the day of OPU outcomes were the overall incidence of OHSS as well as its type and severity, in addition to others pregnancy outcomes data. Results: The occurrence of overall OHSS was significantly lower in calcium infusion group (CIG) than in oral cabergoline group (OCG) [16/115 (13.9%) in CIG versus 32/115 (27.8%)] in OCG with difference in proportion percentage point (D pp) =
13.9% , at 95%CI of
3.38% to
24.10% (P = 0.009) and absolute risk reduction (ARR) in overall OHSS incidence = 13.9% at 95%CI of 3.38–24.10 and relative risk (RR) = 0.5 at 95% CI of 0.29–0.85 (p = 0.012) and relative risk reduction (RRR) = 50% and number need to treatment (NNT) (Benefit) = 7.18 at 95% CI of 4.12 (Benefit) to 28.05 (Benefit)]. Also the incidence of Moderate OHSS was significantly lower in CIG than OCG [2/115 (1.7 %) vs 10/115 (8.6%), p = 0.01] as well as RR of severe OHSS with CI to OC = 0.25 at 95%CI of 0.02–2.20 and RRR of severe OHSS with CI to OC was 75% as it occurred in 4 cases (3.4%) in OCG versus one case (0.8%) in CIG, where this reduction is of great clinical significant despite it does not reach statistical significance (P = 0.17), at NNT (Benefit) = 38.33 at 95% CI of 87.292 (Harm) to 1