Background: Polycystic ovarian syndrome (PCOS) is one of the pathological factors involved in low-quality oocytes, em- bryos and the failure of in vitro fertilization (IVF) and intracy- toplasmic sperm injection (ICSI). Studies have shown improv- ing metabolic–endocrine factors in these patients may increase the quality of oocytes and embryos. On the other hand, there is a growing interest in the use of insulin sensitizer drugs and type 2 diabetes in the treatment of PCOS and researches in re- cent years have shown that metformin and sitagliptin has been reported to improve ovarian cycles and ovulation in PCOS pa- tients. We aimed to compare the effects of metformin and sit- agliptin on oocytes and embryo quality in PCOS individuals undergoing ICSI. Materials and Methods: In this clinical trial, 60 infertile PCOS patients were selected based on the Rotterdam crite- ria; Then they were divided into 3 groups (n=20): metformin group (Glucophage, Merck, West Drayton, UK; 500 mg, twice a day), sitagliptin group (Januvia, Merck, West Drayton, UK; 50 mg, twice a day) and placebo group. All patients were un- dergoing treatment with antagonist GnRH protocol. Treatment was carried out two months before the start of the ovulation cycle and continued until the day of oocyte aspiration. Mature (MII) oocytes were identified by the presence of the first po- lar body under a stereomicroscope (Olympus, Tokyo, Japan). Only those oocytes that had extruded the first polar body (MII oocyte) were used for ICSI. The number of immature oocytes [(Germinal vesicle (GV) and metaphase I (MI)] were counted. Four hours after oocyte retrieval, a single motile sperm with an apparently normal morphology was immobilized and used to inseminate the oocyte. Fertilization was assessed the next day by the presence of two pronuclei (2PN). Embryo quality was assessed on the 3rd day of insemination and graded as follows: Grade I, symmetric blastomeres and no fragmentation; Grade II, unequal blastomeres and
