en Original Article Original Article - <strong>Background:</strong> Embryo transfer (ET) has traditionally been performed two days after oocyte retrieval. Delaying transfer from day two to day three or four would allow for further development of the embryo might therefore optimize the selection of viable and best quality embryos for transfer and may be closer to the physiological time of the entry into the uterus than transfer on day two and might have a positive effect on pregnancy outcomes.<br> <strong>Objective:</strong> The study aimed to determine whether delayed transfer of embryos from 2 to 3 or 4 days after oocyte retrieval and the pregnancy rate in ICSI (intra cytoplasmic sperm injection) procedure.<br> <strong>Materials and Methods:</strong> In this deh1ive study we evaluated infertile couples who were referred to the Mehr Infertility Institute between 2006 and 2008 for ICSI according to the day of embryo transfer. We compared embryo quality pregnancy rate and implantation rate among day 2 3 or 4 of transfers. Pregnancy rate was confirmed by measurement of <span new="" roman="" style="font-size: 12pt; font-family: " times="">&beta;</span>-hCG in serum after 14 days. After data collection analysis was carried out with the t-test and chi squared tests by using the statistical software package SPSS.16.<br> <strong>Results: </strong>The overall clinical pregnancy rate (CPR) reported was 46.6%. The mean age of women and duration of infertility didn^,t differ on the day of embryo transfer (p>0.05). Overall CPRs were not statistically different for day 2 (50.3%) day 3 (46.5%) and day 4 (34.8%) transfers respectively there were no significant differences in the age of transferred embryos between pregnant and nonpregnant women (p>0.05).<br> <strong>Conclusion:</strong> From the result of the present study there were no statistically significant differences in pregnancy rates according to the day of embryo transfer. Embryo transfer, Transfer day, Pregnancy rate, ICSI 135 140 http://ijrm.ir/browse.php?a_code=A-10-549-224&slc_lang=en&sid=1 Fattaneh Farifteh f.farifteh@yahoo.com Yes Mehr Infertility Institute, Rasht, Iran Marzieh Mehrafza No Mehr Infertility Institute, Rasht, Iran Mona Oudi No Mehr Infertility Institute, Rasht, Iran Azadeh Eftekhari No Mehr Infertility Institute, Rasht, Iran Maryam Rahnavard No Mehr Infertility Institute, Rasht, Iran Khatereh Barjasteh No Mehr Infertility Institute, Rasht, Iran Ahmad Hossieni No Mehr Infertility Institute, Rasht, Iran