The role of embryo growth rate in vitro as an isolated indicator of embryo quality in IVF was evaluated retrospectively.Comparison was made between 98 cycles (group 1), in which only embryos at a cleavage stage of two to three blastomers were transferred, and 99 cycles (group 2), in which all embryos were transferred at a cleavage stage of four or more blastomers. Embryos were transferred at a fixed interval of 42 to 44 h following oocyte insemination. The mean patients' age, number of oocytes recovered and number of embryos transferred per cycle were similar in both groups.The pregnancy rate and the take-home-baby rate were significantly higher in group 2 as compared to group 1 (22.2% vs 7.1% and 16.2% vs 4.1%; P < 0.05 and P < 0.001, respectively).These results demonstrate that embryos with a slow cleavage rate in vitro are less likely to produce pregnancy following IVF-ET and that the cleavage stage is a valuable criteria in the selection of the best embryo for transfer.