The causes of infertility may either belong to the man or the woman. However, no problems can be identified in 15% of the couples presenting for an evaluation. This is a condition called unexplained infertility, in which assisted reproductive techniques help achieve pregnancy. Also, there may be only one factor causing infertility or there may be more than one. The causes of infertility can be listed under two categories: male and female factors of infertility. The causes of infertilityare distributed equally between the two genders at a rate of 40% in men and 40% in women in general. In the remaining 15-20% of couples, pregnancy cannot be achieved although no causes can be detected.