Objective: To compare the implantation and pregnancy rates after cleavage stage embryo transfer (ET) with transfer of blastocyststage (days 5-6) embryos. Study design: Prospective randomized trial at an assisted reproduction unit in a university hospital. Women with six or more follicles at the last ultrasound scan before oocyte aspiration were randomized for transfer of a maximum of two embryos after 2-3 days (n = 80) or after 5-6 days (n = 64) of culture. Embryo quality, implantation and pregnancy rates were evaluated. Statistical significance was tested with the Chisquare test and Fishers exact test. Result(s): No significant difference was observed in implantation rates (21.1%versus 20.9%, respectively) and clinical pregnancy rates (36.7%versus 32.5%respectively) after blastocyst and cleavage stage transfers for the two groups. The pregnancy rate among subjects who had at least one good quality embryo transferred was 37.5%per day 2-3 ET and 60%per day 5-6 ET. Conclusion(s): The overall implantation and pregnancy rates after embryo transfer at cleavage stage and at blastocyst stage transfer were not statistically different. Women who had at least one good quality blastocyst (n = 25) had a high pregnancy rate (60%per ET). Blastocyst transfer is a good alternative for couples with many good quality embryos on day 2 after insemination.
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