Cryopreservation: the problem of evaluation.

A simple evaluatory formula for reporting pregnancy rates involving cryopreserved material has so far remained elusive. It is highly desirable to have a method which would allow not only an evaluation of cryotechnology per se, but also an evaluation of the role of cryotechnology in enhancing the total reproductive potential of a single cycle. In this paper, nine separate formulae are described which can be used for the evaluation of cryopreservation. It is concluded that none of the existing formulae used alone expresses the total potential of cryopreservation, and that while each formula provides information regarding some aspect of the role of cryopreservation, the most comprehensive evaluation requires the answer to five different equations. The other four formulae, while often used, are regarded as providing information which is unsubstantiated or does not allow complete evaluation.