Fertility evaluation of frozen/thawed semen

In vitro semen analyses have been used for more than half a century to estimate the fertilizing potential of a semen sample. Unfortunately, none of the assays developed provide results that consistently correlate well with fertility. The reasons for this lack of consistency, due in part to the complexity of the spermatozoon itself, the collection of fertility data, and factors beyond control of the semen analyses themselves, are discussed. Different spermatozoal attributes that are necessary for a spermatozoon to fertilize an oocyte are presented and assays used to evaluate each attribute described. Although laboratory assay results do not correlate well with semen fertility, the importance of conducting laboratory assays on every semen sample used for artificial insemination or to attempt to determine causes for infertility, is discussed.