Objective: To employ protocols of mild ovarian stimulation to prevent an excessively elevated rate of high- order multiple pregnancies. Design: Case series. Setting: University hospital. Patient(s): Six hundred and twenty one consecutive patients undergoing 1,259 controlled ovarian hyperstimulation and intrauterine insemination cycles. Intervention(s): Patients received 50 IU per day of recombinant follicle- stimulating hormone (FSH) starting the third day of the cycle, then a gonadotropin- releasing hormone (GnRH) antagonist on the day in which a follicle<13 mm was visualized. Cycles were canceled if three or more follicles < 16 mm and/or five or more follicles < 11 mm were detected. Main Outcome Measure(s): Rate of high- order multiple pregnancies. Result(s): The clinical pregnancy rate per initiated cycle was 9.2% (95% confidence interval, 7.5- 11.1% ). The incidence of twins and high- order multiple pregnancies was 9.5% (95% CI, 5.3- 16.2% ) and 0 (0.0- 3.2% ), respectively. Conclusion(s): In controlled ovarian hyperstimulation and intrauterine insemination cycles, a protocol of 50 IU of recombinant FSH daily combined with the use of GnRH antagonists and a policy of strict cancellation based on echographic criteria are associated with a satisfactory pregnancy rate per initiated cycle and a low risk of high- order multiple pregnancies. Objective: To employ protocols of mild ovarian stimulation to prevent an excessively elevated rate of high- order multiple pregnancies. Design: Case series. Setting: University hospital. Patient (s): Six hundred and twenty one consecutive patients undergoing 1,259 controlled ovarian hyperstimulation and Intervention (s): Patients received 50 IU per day of recombinant follicle-stimulating hormone (FSH) starting the third day of the cycle, then a gonadotropin-releasing hormone (GnRH) antagonist on the day in which a follicle < 13 mm was visualized. Cycles were canceled if three or more follicles <16 mm and / or five or more follicles <11 mm were detected. Main Outcome Measure (s): Rate of high- order multiple pregnancies. Result (s): The The incidence of twins and high order multiple pregnancies was 9.5% (95% CI, 5.3-16.2%) and 0 (0.0-3.2 %), respectively. Conclu sion (s): In controlled ovarian hyperstimulation and intrauterine insemination cycles, a protocol of 50 IU of recombinant FSH daily combined with the use of GnRH antagonists and a policy of strict cancellation based on echographic criteria are associated with a satisfactory pregnancy rate perired cycle and a low risk of high- order multiple pregnancies.