Contribution of the male factor to unexplained infertility: a review

The more exhaustive the evaluation of couples with unexplained infertility, the more likely is the opportunity for detecting the aetiological factor responsible for infertility. Transport of spermatozoa through the upper genital tract and their ability to fertilize the oocyte are two obscure areas for the conventional evaluation of infertility. Although research in the former area is limited, there is indirect evidence that impaired sperm transport could be one of the causes of infertility in some couples with otherwise unexplained infertility. On the other hand, the availability of sperm function tests and the correlation of their results with in-vitro fertilization rates have allowed the detection of a previously hidden male factor in couples with unexplained infertility. It has been demonstrated that couples suffering unexplained infertility have significantly lower in-vitro fertilization rates in comparison with patients with tubal problems. These results can be explained because several case control studies in patients with unexplained infertility have reported defects in capacitation and sperm motion characteristics, binding of the spermatozoa to the zona pellucida, acrosome reaction, acrosin activity of the spermatozoa, and the ability of the spermatozoa to penetrate zona-free hamster cocytes. These observations suggest that methods for assessing the fertilizing capacity of the spermatozoa have to be incorporated in the evaluation of couples with unexplained infertility in order to amplify the scope of the workup and to better decide the appropiate treatment for these couples.