This study on the epidemiology of human fertility emphasizes the study and analysis of several parameters. These include: the measure and distribution of fertility. The incidence of sterility is low (3-5% of couples) and the fecundability of fertile couples is approximately 30% per cycle. Approximately 7% of newly-formed couples per year will undergo complex treatment for infertility. The results of clinical and diagnostic explorations. Among infertile couples, the woman is responsible in approximately 60% of cases, and the man in approximately 25% of cases, and both of these factors may be associated. Clinical and diagnostic explorations are negative in approximately 18% of couples and the infertility is termed idiopathic. 'Normal' sperm characteristics vary according to age, seasonal or environmental factors. Female factors varying as a function of age, menstrual cycle, ovulation and functional status of the genital organs. Infertility in both partners leads to specific difficulties for epidemiological analyses, where the base unit is not an individual.