ABSTRACT
There is a widespread belief that the results of TI of cryopreserved sperm are poorer than with fresh semen/sperm. In fact, comparative studies have not consistently supported this view and, while some studies give support to this view, others deny it (see Table 1). Expressed as cumulative insemination cycles, pregnancy rates have been reported to be as high as 70-75%, with a miscarriage rate of 15-16% and a mean number of 3.5 cycles to conception. There are many factors that can affect
pregnancy success rates and the effect of cryopreservation per se may be small compared with the other variables. It is also important to note that there is considerable variation in tolerance to freeze-thawing between semen specimens, and this is as true of animal species as it is of humans28. There is greater consistency between specimens from the same individual than between males29. As a rule of thumb, about a third of men produce specimens that cryopreserve very successfully, a third are rather unsuccessful and another third are intermediate (personal experience of 15 years). Thus, frozen banking of sperm
does not provide assurance for a young cancer sufferer that his semen will cryopreserve successfully, and, of course, his medical condition may prevent him from producing a good or any specimen in time30. These differences may be reflected in the plasma membrane susceptibility/properties of the spermatozoa, but at present there is no reliable way of predicting which individuals will be most successful, except on the basis of previous history of cryopreservation and, partially, on the motility of sperm in the semen sample being cryopreserved. In our experience, samples with sperm motilities of >60% have a better chance of effective cryopreservation than samples with lower motilities. One of the conclusions from such observations is that no single freeze-thaw protocol is ideal for all individuals.
