A computer implemented method of ranking IVF embryos to predict their development potential after transfer; the method comprising: obtaining values for a plurality of characteristics relating to the morphological development of the embryos during an observation period; determining for respective ones of the embryos a measure of whether or not the embryo has undergone a direct cleavage event, and ranking the embryos determined to have undergone a direct cleavage event with a ranking that indicates a lower development potential than for the embryos not determined to have undergone a direct cleavage event; and for the embryos not determined to have undergone a direct cleavage event, determining whether or not a measure of a duration of a predefined developmental stage for the embryo exceeds a predefined threshold duration, and ranking embryos for which the duration of the predefined developmental stage is determined to exceed the predefined threshold duration with a ranking that indicates a lower development potential than for the embryos for which the duration of the predefined developmental stage is not determined to exceed the predefined threshold duration; and for the embryos for which the duration of the predefined developmental stage is not determined to exceed the predefined threshold duration, determining whether or not a measure of a relative duration of a first predefined developmental stage for the embryo with respect to a second predefined developmental stage for the embryo is outside a predefined range, and ranking embryos for which the relative duration is outside the predefined range with a ranking that indicates a lower development potential than for the embryos for which the relative duration of is not outside the predefined range. obtaining values for a plurality of characteristics relating to the morphological development of the embryos during an observation period; determining for respective ones of the embryos a measure of whether or not the embryo has undergone a direct cleavage event, and ranking the embryos determined to have undergone a direct cleavage event with a ranking that indicates a lower development potential than for the embryos not determined to have undergone a direct cleavage event; and for the embryos not determined to have undergone a direct cleavage event, determining whether or not a measure of a duration of a predefined developmental stage for the embryo exceeds a predefined threshold duration, and ranking embryos for which the duration of the predefined developmental stage is determined to exceed the predefined threshold duration with a ranking that indicates a lower development potential than for the embryos for which the duration of the predefined developmental stage is not determined to exceed the predefined threshold duration; and for the embryos for which the duration of the predefined developmental stage is not determined to exceed the predefined threshold duration, determining whether or not a measure of a relative duration of a first predefined developmental stage for the embryo with respect to a second predefined developmental stage for the embryo is outside a predefined range, and ranking embryos for which the relative duration is outside the predefined range with a ranking that indicates a lower development potential than for the embryos for which the relative duration of is not outside the predefined range. <EOS>