Methods and systems for measuring and using the oxidation-reduction potential (ORP) of a biological sample are provided. The system generally includes a test strip and a readout device for determining the ORP. The measured ORP is then used to determine characteristics relating to the fertility of the sample or the subject from which the sample was derived. Some characteristics that can be determined include the quality of a sperm sample, an oocyte or a fertilized egg. The measured ORP value can also be used to determine the specific characteristics of a spermatozoa sample, such as the morphology of the spermatozoa, the motility of the spermatozoa, the number of cells in the sample and the concentration of the cells in the sample. Knowledge of such characteristics and fertility potential can be used to identify individuals that might benefit from specific fertility treatments.