Objective To assess the efficacy of adding Gn-releasing hormone antagonist(GnR HA) on the day of hC G triggering in a long luteal protocol without withholding the agonist in women who are at a risk to develop ovarian hyperstimulation syndrome(OHSS).Methods This was a retrospective cohort study conducted upon 50 women who have elevated serum estradiol(E_2) level >4 500 ng/L at the day of ovum triggering with hC G on a long agonist luteal protocol of controlled ovarian stimulation(COS). When an exaggerated ovarian response was observed around day 10 of stimulation, immediately the next morning at 6 a.m. gonadotropin administration was stopped or reduced, and a single dose of ganirelix acetate(antagonist) was given sc continuation of the agonist dose hC G. Another serum E_2 measurement was done at 6 p.m.(after 12 h of antagonist) then hC G, sc 250 mg and choriogonadotropin α were administered 14 h later after antagonist and documented the reduction of E_2 level. Oocyte retrieval was conducted after 34-36 h of hC G administration. The measured outcomes were the level of E_2 on the day of hC G injection, number of oocytes and their quality, pregnancy rate and the occurrence of OHSS and its grade in case it happened.Results The total dose for recombinant FSH was 25.3±6.4 ampoules(75 IU/ampoule) while it was 11.0±3.0 ampoules for the urinary hM G. A higher oocyte maturation rate(82.8%) and a high fertilization rate(87.8%) were observed. The mean endometrial thickness was 10.1±1.0 mm on the day of hC G triggering. The higher fertilization rate with the good endometrial thickness observed resulting in a higher pregnancy rate(78.0%, 39/50) with statistically significant(P<0.05). A significant reduction of E_2 level was documented by a percentage around 40% before hC Ginjection. There were no reported cases of severe or moderate OHSS, however 13 cases(26%) were reported to have mild OHSS constituting.Conclusion Acceleration of coasting in cases of OHSS through treatment with GnR HA after pituitary suppression with GnR H agonist(GnR H-a) offered a novel approach to decrease E_2 level, avoided cycle cancellation, and maintain excellent oocyte maturation rate, and finally result in high pregnancy rate with prevention of OHSS. Objective To assess the efficacy of adding Gn-releasing hormone antagonist (GnR HA) on the day of hC G triggering in a long luteal protocol without withholding the agonist in women who are at risk a develop ovarian hyperstimulation syndrome (OHSS). Methods This was a retrospective cohort study conducted upon 50 women who had elevated serum estradiol (E2) level> 4 500 ng / L at the day of ovum triggering with hC G on a long agonist luteal protocol of controlled ovarian stimulation (COS). When an exaggerated ovarian response was observed around day 10 of stimulation, immediately the next morning at 6 am gonadotropin administration was stopped or reduced, and a single dose of ganirelix acetate (antagonist) was given sc continuation of the agonist dose hC G. Another serum E_2 measurement was done at 6 pm (after 12 h of antagonist) then hC G, sc 250 mg and choriogonadotropin α were administered 14 h later after antagonist and documented the reduction of E_2 level. Oocyte retrieval was cond ucted after 34-36 h of hC G administration. The measured outcomes were the level of E_2 on the day of hC G injection, number of oocytes and their quality, pregnancy rate and the occurrence of OHSS and its grade in case it happened. Results The total dose of recombinant FSH was 25.3 ± 6.4 ampoules (75 IU / ampoule) while it was 11.0 ± 3.0 ampoules for the urinary hM G. A higher oocyte maturation rate (82.8%) and a high fertilization rate (87.8%) were observed The mean endometrial thickness was 10.1 ± 1.0 mm on the day of hC G triggering. The higher fertilization rate with the good endometrial thickness observed resulted in a higher pregnancy rate (78.0%, 39/50) with statistically significant (P <0.05) . A significant reduction of E_2 level was documented by a percentage around a 40% before hC Ginjection. There were no reported cases of severe or moderate OHSS, however 13 cases (26%) were reported to have mild OHSS constituted. Confluence Acceleration of coasting in cases of OHSS through treatment wi th GnR HA after pituitary suppression with GnR H agonist (GnR H-a) offered a novel approach to decrease E_2 level, avoided cycle cancellation, and maintain excellent oocyte maturation rate, and finally result in high pregnancy rate with prevention of OHSS.