implantation loss (2-4). Recent studies provide a growing body of evidence on significant association between ovarian stimulation and increased incidence of certain imprinting diseases including Beckwith-Wiedemann and Angelman syndromes in humans as well as imprinting defects in the mice (5,6). Methylation marks established on imprinted genes in the mouse are stably preserved during the second wave of genome-wide demethylation and remethylation occurs in the late blastocyst close to the time of implantation to maintain sex-specific monoallelic expression of gene imprints (7,8). The establishment, maintenance, or acquisition of methylation marks during epigenetic reprogramming are thought to be vulnerable to some degree of error and may be disrupted due to various factors including exposure to certain environmental factors such as high doses of exogenous gonadotrophins (4,6). The hypothesis of the epigenetic effects of superovulation are supported by several detailed reports showing aberrant DNA methylation of imprinted genes Abstract Objectives: In this experiment, possible effect of superovulation on important molecular profiles of oocytes and embryos were examined in mice regarding their development. Materials and Methods: A total of 120 metaphase II oocytes were produced by super or spontaneous ovulation. Blastocyst-stage embryos were produced after in vitro fertilization (IVF) and in vivo fertilization. Blastocysts that have been obtained from naturally mated female without gonadotrophin treatment were also used as controls. Using real-time polymerase chain reaction (PCR), the mRNA expression patterns of Bone morphogenesis protein (Bmp 15(, hepatoma-derived growth factor (Hdgf(, DNA methyl transpherase-1 (Dnmt-1), developmental pluripotency associated 3 (Dppa3(, and zinc finger protein 57 (Zfp57(genes were compared between superovulated and spontaneously ovulated oocytes; the expression patterns of H19 and small nuclear ribonucleoprotein N(Snrpn) imprinting genes between embryos produced from these oocytes were also compared. Results: The results of the study showed that expression of five maternal effect genes (Bmp15, Hdgf, Dnmt-1, Dppa3, and Zfp57) in superovulated oocytes were significantly reduced (P<0.05). However, the rates of cleavage to the blastocyst stages were not significantly different (P<0.05) between superovulated and naturally ovulated oocytes in cultured embryos. Moreover, superovulation disturbed the expression patterns of imprinting genes (H19 and Snrpn) in single blastocysts obtained by different assisted reproductive techniques (ARTs). Conclusions: The findings indicated that superovulation affected the molecular characteristics of ART conceived embryos.