The present invention relates to a method and to a system for selecting embryos for in vitro fertilization based on the timing, and duration of observed cell cleavages and associated cell morphology. One embodiment of the invention relates to a method for determining embryo quality comprising monitoring the embryo for a time period, and determining one or more quality criteria for said embryo, wherein said one or more quality criteria is based on the extent of irregularity of the timing of cell divisions when the embryo develops from four to eight blastomeres, and/or wherein said one or more quality criteria is based on determining the time of cleavage to a five blastomere embryo (t5) and wherein t5 is between 48.7 hours and 55.6 hours, and/or wherein said one or more quality criteria is based on the ratio of two time intervals, each of said two time intervals determined as the duration of a time period between two morphological events in the embryo development from fertilization to eight blastomeres, and based on said one or more quality criteria determining the embryo quality.