Semen characteristics and fertility tests required for storage of spermatozoa.

This review addresses critical issues in the selection of semen donors who are very fertile. Traditional semen parameters have been employed and are still used to assess pre- and post-freeze samples in order to discriminate between donors of high and low fecundity. The most predictive factor is the number of motile spermatozoa per straw and the number of motile spermatozoa inseminated. Nevertheless, no absolute standards for fertile samples can be derived from the basic semen examination. The employment of sperm function testing such as the hamster penetration test or computerized motility analysis has been shown to enhance moderately the prediction of fertility of semen samples however, further studies are necessary to determine if these improvements are clinically useful. The need to determine with a high degree of confidence the fecundity of donor semen is enhanced by limitations in the number of pregnancies allowed per donor. The recent publication of league tables in the UK has put extra pressure in clinics to use highly fertile donors. Spermatozoa are also cryostored for patients prior to cancer treatment. With the development of intracytoplasmic sperm injection every sample produced by cancer patients can be stored irrespective of the quality. However, several factors need to be elucidated to maximize the fertility of those patients. The establishment of regional centres in Europe will be a good starting point to deal with many of the issues raised in this review.