Received November 16, 2013
Accepted November 16, 2013

OBJECTIVE: To establish morphologic criteria for blastocyst selection to decide single embryo transfer. Methods: Retrospective analysis of database from January 2006 to December 2011. One hundred and twenty eight women in 135 cycles on day five embryo transfer were included (1020 zygotes from 135 oocyte retrievals were followed from day one to five and morphological criteria were evaluated). To assess differences between groups, Student’s t test and chi-squared test were used, and Odds ratio with CI 95% determined significant associations. RESULTS: Overall results of 135 cycles with transfer on day five showed 47.4% clinical pregnancy rate (CPR) per cycle, 31.0% implantation rate (IR), 37.5% multiple pregnancy rate (MPR) and 7.5% miscarriage rates (MR). 74 cycles in which >2 embryos reached the blastocyst stage allowed selection for transfer and also cryopreservation with 60.8% CPR, 42.3% IR, 40.0% MPR and 6.6% MR (compared with the total population, statistical difference was observed only in the IR (p = 0.0456). On 30 cycles that patients were transferred with only expanded blastocyst on day 5 showed 76.7% CPR, 56.7% IR, 43.5% MPR and 4.34% MR while 70 cycles of non-expanded blastocyst transfers showed 35.7% CPR, 24.2% IR, 44.0% MPR and 12.0% MR. Statistical difference was observed in the CPR (p< 0.0001) and IR (p < 0.0001) comparing expanded and not expanded transfers. CONCLUSION: In selected cases, single blastocyst transfer can be performed with high implantation and clinical pregnancy rates. Four good quality embryos on day 3 will benefit from transfer at the blastocyst stage.