Objective: Progestins are used as an alternative to gonadotropin releasing hormone (GnRH) antagonists to suppress premature luteinizing hormone (LH) surge and a flexible protocol has been defined recently. The aim of this study was to compare the efficacy of flexible protocols with dydrogesterone and GnRH antagonist in suppressing LH surge. Material and Methods: This retrospective, case-control study, was conducted in an infertility unit of a tertiary university hospital. A daily dose of 40 mg dydrogesterone was compared with GnRH antagonist (GnRHant) in controlled ovarian hyperstimulation cycles between July 2018 and July 2019. Dydrogesterone was started when the leading follicle was 12 mm or serum estradiol was over 300 pg/mL. A subgroup analysis of poor responder patients was also performed. Results: In total there were 105 subjects aged between 23 and 41 years, 52 in the dydrogesterone group and 53 in the GnRHant group. Duration of pituitary suppression was longer in dydrogesterone group. Premature ovulation was observed in 11.5% (6/52) and 0% in the dydrogesterone and GnRHant groups, respectively. However, collected oocyte counts and metaphase II oocyte counts were found to be similar between the groups. The six patients with premature ovulation were in poor responder subgroup. Conclusion: Dydrogesterone can be used as an alternative to antagonist regimen in patients where embryo transfer is not planned in the same cycle. However, flexible regimen may not be appropriate in patients with diminished ovarian reserve, as advanced follicular maturation and delayed suppressive effect of oral progesterone may cause premature ovulation. Randomized controlled trials in particular patient groups are required to determine the most effective minimum dose and time of application to ensure treatment success. (J Turk Ger Gynecol Assoc 2021; 22: 293-9)